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Posterior inferior cerebellar artery

aneurysms: An institutional series

 

                                                       

 

Thesis submitted in fulfillment of the rules and regulations for MCh Degree Examination of Sree

Chitra Tirunal Institute for Medical Sciences and Technology, Thiruvananthapuram

By

Dr. Manish Ganesh Pai

Resident in Neurosurgery

Month and Year of Submission: October 2011

 

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CERTIFICATE

This is to certify that the thesis entitled “Posterior inferior cerebellar artery

aneurysms: An institutional series” is a bonafide work of Dr. Manish Ganesh

Pai and was conducted in the Department of Neurosurgery, Sree Chitra

Tirunal Institute for Medical Sciences & Technology, Thiruvananthapuram

(SCTIMST), under my guidance and supervision.

Dr. Suresh Nair

Professor and Head

Department of Neurosurgery

SCTIMST, Thiruvananthapuram

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DECLARATION

This thesis titled “Posterior inferior cerebellar artery aneurysms: An

institutional series” is a consolidated report based on a bonafide study

done by me during the period from January 2009 to September 2011,

under the Department of Neurosurgery, Sree Chitra Tirunal Institute for

Medical Sciences & Technology, Thiruvananthapuram.

This thesis is submitted to SCTIMST in partial fulfillment of rules and

regulations of MCh Neurosurgery examination.

Dr. Manish Ganesh Pai

Department of Neurosurgery,

SCTIMST, Thiruvananthapuram.

 

 

 

 

 

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ACKNOWLEDGEMENT

The guidance of Dr. Suresh Nair, Professor and Head of the Department of Neurosurgery, has been invaluable and I am extremely grateful and indebted for his contributions and suggestions, which were of invaluable help during the entire work. He will always be a constant source of inspiration to me.

I owe a deep sense of gratitude to Dr. Girish Menon for his invaluable advice, encouragement and guidance, without which this work would not have been possible.

The critical remarks, suggestions of Dr. Gopalakrishnan C. V, helped me in achieving a high standard of work.

I am deeply indebted to Dr. Mathew Abraham, Dr. Easwer H. V, Dr. Krishnakumar K, Dr. George Vilanilam, Dr. Jayanand Sudhir and thank them for their constant encouragement and support.

I wish to sincerely thank all my colleagues for their support.

Last but not the least, I owe a deep sense of gratitude to all my patients without whom this work would not have been possible.

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INDEX

INTRODUCTION 7-8

REVIEW OF LITERATURE 9-60

AIMS AND OBJECTIVES 61

MATERIALS AND METHODS 62

RESULTS 63-74

DISCUSSION 75-96

CONCLUSIONS 97-98

REFERENCES 99-109

PROFORMA 110-111

ABBREVIATIONS 112-113

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INTRODUCTION

Aneurysms arising from the posterior inferior cerebellar artery (PICA),

either at its junction with the vertebral artery or more peripherally along

its course, are rare, representing approximately 0.49% of intracranial

aneurysms (1). Aneurysms of the PICA-VA complex combine a narrow

range of clinical presentation with unusual anatomical variability. Their

strategic location and the tortuousness of the vertebral arteries require

special consideration during diagnostic evaluation and surgical planning.

Aneurysms of the vertebrobasilar system have several characteristic

features which distinguish them from aneurysms of the anterior

circulation. First of all, they are relatively uncommon, accounting for

only about 3% of the intracranial aneurysms. This is the reason why the

majority of neurosurgeons have little experience with the management of

these lesions. Secondly, these aneurysms show great variability in size,

location, and morphology. The percentage of dissecting and fusiform

aneurysms is much higher than in the other intracranial compartments.

Thirdly, most of the aneurysms of the vertebral artery (VA) and the

posterior inferior cerebellar artery (PICA) are located deeply in the

posterior fossa and have a close relationship to the lower brainstem and

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the caudal cranial nerves. The variability of the anatomy of the VA and

the PICA add further to the complexity of the lesions and increase the

risk of surgical management (2). It is sometimes even difficult to pick the

side from which the surgical approach should be made, unless the

angiographic size and delineation of the aneurysm, the general height and

shape of the vertebral artery, and the pattern of collateral supply are

carefully evaluated. Relatively little guidance is available in the literature

in regard to these matters. Posterior inferior cerebellar artery (PICA)

aneurysms are uncommon and their underlying pathology, natural history

and clinical management are poorly understood. Surgical treatment of

PICA aneurysms is challenging in view of their close neurovascular

relationship. Evaluation of these aneurysms with relation to outcome after

treatment is scant in the neurosurgical literature. Analysis of outcome is

critical, however, if surgeons are to understand the likely consequences of

their actions.

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REVIEW OF LITERATURE

Incidence

Aneurysms arising from the posteroinferior cerebellar artery (PICA),

either at its junction with the vertebral artery or more peripherally along

its course, are rare. Vertebrobasilar aneurysms constitute approximately

15% of all intracranial aneurysms, most of which arise from the

basilar apex (3). VA aneurysms represent 20 to 30% of posterior fossa

aneurysms. One-fifth of these posterior fossa lesions originate from

the posterior inferior cerebellar artery (PICA), thus accounting for

3% of all intracranial aneurysms (4). Aneurysms that arise at the PICA-

VA complex are relatively uncommon, comprising less than 0.5% to 3%

of all intracranial aneurysms (5).

In a cooperative study of 2672 intracranial aneurysms, the incidence of

PICA aneurysms was 0.49% (1). In a study by McDonald and Korb (6) in

1939 the incidence of PICA aneurysms was reported as 0.8%. Majority of

the aneurysms on the vertebral artery arise at the origin of the PICA (7).

Aneurysms of the PICA are usually found on the bifurcation of the

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vertebral artery-PICA junction (4, 8). Aneurysms arising from the

peripheral segment of the PICA are quite rare. Distal PICA aneurysms are

relatively rare, constituting less than 30% of all PICA aneurysms (4, 8, 9,

10). Aneurysms arising on the PICA distal to the origin represent only 0.5

to 1 % of all intracranial aneurysms (7, 11). Rothman et al. noted that two

thirds of aneurysms involving the PICA arose at the origin and one-third

arose distal to the origin (11). PICA-vertebral aneurysms usually arise

along the rostral one-half of the origin of the PICA, point superiorly and

slightly posteriorly, and lay against the medulla (7, 12, 13). Rarely, the

PICA-vertebral junction may be the site of a dissecting aneurysm (14,

15).

Historical Perspective

Cruveilhier described a spherical aneurysm arising from the PICA-

vertebral junction in 1829 (16). Fernet (17) reported the first case of an

aneurysm arising from a distal segment of the PICA in 1864. But it was

not until 1947 that Rizzoli and Hayes (18) performed the first surgical

procedure on an aneurysm known to arise from this vessel. In their case,

preoperative angiography was not done, and the posterior fossa location

of the lesion was deduced from a shift of the fourth ventricle seen at

ventriculography. The aneurysm was trapped between silver clips.

Schwartz reported the first successful obliteration of a posterior fossa

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aneurysm in 1948 (19). The rare peripheral PICA aneurysm was first

operated by Olivecrona in 1932(20). Richardson's study (21) of the

natural history of aneurysms following SAH revealed that those arising

from the vertebrobasilar system were associated with the highest

mortality rate. Uihlein and Hughes (22) reported a series of 14 posterior

fossa aneurysms treated without definitive surgery; eight of these patients

died of aneurysm rupture. Routine utilization of vertebral angiography

after normal carotid angiography in patients with SAH enhanced the

recognition of these aneurysms. In 1958, DeSaussure, et al., reported the

successful trapping of two PICA aneurysms that had been defined by

preoperative angiography (23). Further refinements, including

transfemoral catheterization, subtraction, and magnification, have

enhanced the preoperative angiographic assessment of size, location,

and position of such aneurysms. In 1967, Rand and Jannetta (24)

recognized the benefit of the operating microscope for aneurysms of

the vertebrobasilar system, both for the delicate dissection of the neck

of the aneurysm and for preventing inadvertent occlusion of the small

perforating arteries at the time of clipping. The excellent results enjoyed

by Drake (25) and others confirm these benefits.

ANATOMY OF PICA (26, 27)

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The PICA has the most complex, tortuous, and variable course and area

of supply of the cerebellar arteries. It may be exposed in surgical

approaches to the foramen magnum, fourth ventricle, cerebellar

hemisphere, brainstem, jugular foramen, cerebellopontine angle, petrous

apex, clivus and trigeminal nerve (26). The PICA is intimately related to

the cerebellomedullary fissure, the inferior half of the ventricular roof, the

inferior cerebellar peduncle, and the suboccipital surface.

Origin of the PICA and its course (26, 27):

The PICA, by definition, arises from the vertebral artery near the inferior

olive and passes posteriorly around the medulla. Warwick and Williams

in Gray’s Anatomy have also defined the PICA as arising solely from the

vertebral artery (28). The PICA is less commonly defined as the

cerebellar artery that supplies the posteroinferior part of the cerebellum

and generally arises from the vertebral artery. The PICA may also arise

from the basilar artery (29, 30).

If a PICA is present, it is the largest branch of the vertebral artery. It is

rarely absent bilaterally, but may arise as a double or duplicate PICA.

Salamon and Huang found the PICA to be absent unilaterally in 26% and

bilaterally in 2% of the brains examined (31). Margolis and Newton

found it to be absent in 15% and double in 2.5% of the brains examined

(32).

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The site of origin of the PICA from the vertebral artery varied in location

from below the foramen magnum to the vertebrobasilar junction. The

origin was located between 14mm below and 26mm above the level of

the foramen magnum (average, 8.6mm above the foramen). A few of the

PICAs arising below the foramen magnum may arise from the vertebral

artery in an extradural location.

The PICA arises from the posterior or lateral surfaces of the vertebral

artery more often than from the medial or anterior surfaces. On leaving

the parent vessel, the initial course of the PICA is posterior, lateral, or

superior more often than anterior,medial, or inferior. The diameter of the

PICA at its origin ranges from 0.5 to 3.4 mm (average, 2.0 mm). The

PICA has been reported to be hypoplastic in 5 to 16% of cerebellar

hemispheres (31, 32).

At the anterolateral margin of the medulla, it passes rostral or caudal to or

between the rootlets of the hypoglossal nerve, and at the posterolateral

margin of the medulla it courses rostral to or between the fila of the

glossopharyngeal, vagus, and accessory nerves. After passing the latter

nerves, it courses around the cerebellar tonsil and enters the

cerebellomedullary fissure and passes posterior to the lower half of the

roof of the fourth ventricle. On exiting the cerebellomedullary fissure, its

branches are distributed to the vermis and hemisphere of the suboccipital

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surface. The medial trunk supplies the vermis and adjacent part of the

hemisphere, and the lateral trunk supplies the cortical surface of the tonsil

and the hemisphere. The PICA gives off perforating, choroidal, and

cortical arteries. The cortical arteries are divided into vermian, tonsillar,

and hemispheric groups.

Segments

The PICA is divided into five segments (26): 1) anterior medullary, 2)

lateral medullary, 3) tonsillo-medullary, 4) telovelotonsillar, and 5)

cortical. These segments are often longer than the distance around the

medulla or the tonsil because the PICA frequently has a tortuous course

and forms complex loops on the side of the brainstem among the lower

cranial nerves, near the tonsil, and caudal to the roof of the fourth

ventricle. Each segment may include more than one trunk, depending on

the level of bifurcation of the artery.

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Figure 1: Drawing demonstrating lateral view of PICA anatomy and

nomenclature. Green portion (1) = anterior medullary segment; orange

portion (2) = lateral medullary segment; blue portion (3) =

tonsillomedullary segment; yellow portion (4) = telovelotonsillary

segment; and red portion (5) =cortical segment.

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Figure 2: Drawing demonstrating posterior view of PICA anatomy and

nomenclature. Green portion (1) = anterior medullary segment; orange

portion (2) = lateral medullary segment; blue portion (3) =

tonsillomedullary segment; yellow portion (4) = telovelotonsillary

segment; and red portion (5) =cortical segment.

Anterior medullary segment

This segment lies anterior to the medulla. It begins at the origin of the

PICA anterior to the medulla and extends backward past the hypoglossal

rootlets to the level of a rostrocaudal line through the most prominent part

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of the inferior olive that marks the boundary between the anterior and

lateral surfaces of the medulla.

Those PICAs arising lateral rather than anterior to the medulla do not

have an anterior medullary segment. An anterior medullary segment is

more likely to be present if the PICA arises from the superior part of the

vertebral artery, because the vertebral artery courses from the lateral side

of the medulla below to the anterior surface of the medulla above. An

anterior medullary segment is present if the vertebral artery at the level of

origin of the PICA has passed to the anterior surface of the brainstem.

From its origin, the PICA usually passes posteriorly around or between

the hypoglossal rootlets, but occasionally loops upward, downward,

laterally, or medially before passing posteriorly around or between the

hypoglossal rootlets.

Lateral medullary segment

This segment begins where the artery passes the most prominent point of

the olive and ends at the level of the origin of the glossopharyngeal,

vagus, and accessory rootlets. This segment is present in most PICAs. Its

course varies from passing directly posterior to reach the

glossopharyngeal, vagal, and accessory rootlets to ascending, descending,

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or passing laterally or medially to form one or more complex loops in the

cistern on the side of the brainstem before passing between these nerves.

Tonsillomedullary segment

This segment begins where the PICA passes posterior to the

glossopharyngeal, vagus, and accessory nerves and extends medially

across the posterior aspect of the medulla near the caudal half of the

tonsil. It ends where the artery ascends to the midlevel of the medial

surface of the tonsil. The proximal portion of this segment usually

courses near the lateral recess and then posteriorly to reach the inferior

pole of the tonsil. This segment commonly passes medially between the

lower margin of the tonsil and the medulla before turning rostrally along

the medial surface of the tonsil.

The loop passing near the lower part of the tonsil, referred to as the

caudal or infratonsillar loop, has been reported to form a caudally convex

loop that coincides with the caudal pole of the tonsil, but it may also

course superior or inferior to the caudal pole of the tonsil without forming

a loop. In some cases it dips below the caudal margin of the tonsil and

even below the level of the foramen magnum. A caudally convex loop is

not present if the PICA passes directly medial between the tonsil and

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medulla, if the PICA ascends along the lateral surface of the tonsil to

reach the hemispheric surface, or if the artery has a low origin from the

vertebral artery and ascends posterior to the medulla to reach the tonsil.

The relationship between the tonsillomedullary segment and the

cerebellar tonsil and foramen magnum varies.

Figure 3: PICAs passage through the cerebellomedullary fissure and

around the tonsil. The artery frequently forms a caudal loop at the lower

margin of the tonsil and a cranial or supratonsillar loop that wraps around

the rostral pole of the tonsil

Telovelotonsillar segment

This is the most complex of the segments. It begins at the midportion of

the PICA’s ascent along the medial surface of the tonsil toward the roof

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of the fourth ventricle and ends where it exits the fissures between the

vermis, tonsil, and hemisphere to reach the suboccipital surface. In most,

but not all, hemispheres, this segment often forms a loop with a convex

rostral curve, called the cranial loop. This loop is located caudal to the

fastigium between the cerebellar tonsil below and the tela choroidea and

posterior medullary velum above. The apex of the cranial loop usually

overlies the central part of the inferior medullary velum. This segment

gives rise to branches that supply the tela choroidea and choroid plexus of

the fourth ventricle.

Cortical segment

This segment begins where the trunks and branches leave the groove

between the vermis medially and the tonsil and the hemisphere laterally,

and includes the terminal cortical branches. The bifurcation of the PICA

often occurs near the origin of this segment. The cortical branches radiate

outward from the superior and lateral borders of the tonsil to the

remainder of the vermis and hemisphere.

Bifurcation

Most PICAs bifurcate into a smaller medial and a larger lateral trunk; the

trunk before the bifurcation is referred to as the main trunk. The medial

trunk supplies the vermis and adjacent part of the hemisphere and the

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lateral trunk supplies most of the hemispheric and tonsillar parts of the

suboccipital surface. The bifurcation usually occurs posterior to the

brainstem as the PICA courses around the tonsil. The most common site

of the bifurcation is in the telovelotonsillar fissure as the artery courses

around the rostral pole of the tonsil. The medial trunk usually ascends in

the vermohemispheric fissure to reach the vermis, and the lateral trunk

passes laterally out of the telovelotonsillar fissure to reach the

hemispheric surface. The medial trunk terminates by sending branches

over the inferior part of the vermis and adjacent part of the tonsil and

hemisphere. The lateral trunk divides into a larger hemispheric trunk that

gives off multiple branches to the hemisphere and smaller tonsillar

branches that supply the posterior and inferior surfaces of the tonsil.

Figure 4: The PICAs divide into a medial trunk, which supplies the

vermis and adjacent part of the hemisphere, and a caudal trunk, which

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loops around the tonsil to supply the largest part of the hemispheric

surface. Choroidal branches pass to the tela choroidea and choroid plexus

in the roof.

Branches

The PICA gives rise to perforating branches to the medulla, choroidal

arteries that supply the tela choroidea and choroid plexus, and cortical

arteries. The cortical arteries are divided into median and paramedian

vermian, tonsillar, and medial, intermediate, and lateral hemispheric

arteries. The cortical branches arising near the superior pole of the tonsil

send branches upward to supply the dentate nucleus.

Perforating arteries

The perforating arteries are small arteries that arise from the three

medullary segments and terminate in the brainstem. They are divided into

direct and circumflex types. The direct type pursues a straight course to

enter the brainstem. The circumflex type passes around the brainstem

before terminating in it.

The circumflex perforating arteries are divided into short and long types.

The short circumflex type does not travel more than 90 degrees around

the circumference of the brainstem. The long circumflex type travels a

greater distance to reach the opposite surface. Both types of circumflex

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arteries send branches into the brainstem along their course. The

perforating arteries have numerous branches and anasto-moses that create

a plexiform pattern on the medullary surface. They terminate in the lateral

and posterior surfaces of the medulla.

The perforating branches of the PICA intermingle and overlap with those

arising from the vertebral artery. The segment of the vertebral artery

distal to the origin of the PICA more frequently gives rise to perforating

arteries than the segment proximal to the PICA origin. The perforating

branches arising between the entrance of the vertebral artery into the dura

mater and origin of the PICA are most commonly of the short circumflex

or direct type and terminate predominately on the lateral side of the

medulla. Those arising between the PICA origin and the vertebrobasilar

junction are predominately of the short circumflex type and terminate on

the anterior and lateral surfaces of the medulla.

Choroidal arteries

The PICA gives rise to branches that supply the tela choroidea and

choroid plexus of the fourth ventricle, usually supplying the choroid

plexus near the midline of the roof of the fourth ventricle and in the

medial part of the lateral recess. This includes all of the medial segment

and the adjacent part of the lateral segment of the choroid plexus. More

choroidal branches arise from the tonsillomedullary and telovelotonsillar

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segments than from the lateral or anterior medullary segment. The

segment of the vertebral artery distal to the PICA origin also gives rise to

a few branches that enter the choroid plexus protruding from the foramen

of Luschka.

Cortical arteries

The most constant area supplied by the PICA includes the majority of the

ipsilateral half of the suboccipital surface of the cerebellum. This includes

the majority of the suboccipital surface of the ipsilateral hemisphere and

tonsil, the ipsilateral half of the vermis, and the anterior aspect of the

tonsil. If the PICA is absent on one side, the contralateral PICA or the

ipsilateral AICA supplies most of the area normally supplied by the

absent PICA.

The cortical branches are divided into hemispheric, vermian, and tonsillar

groups. The vermian branches usually arise from the medial trunk, and

the hemispheric and tonsillar branches from the lateral trunk. Each half of

the vermis is divided into median and paramedian segments, and the

hemisphere lateral to the vermis is divided into medial, intermediate, and

lateral segments. There is a reciprocal relationship with frequent overlap

in the areas supplied by the tonsillar, hemispheric, and vermian branches.

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Hemispheric branches

The hemispheric branches most commonly arise from the lateral trunk

within or distal to the vermo-hemispheric fissure. They appear to radiate

outward to the hemispheric surface from the superior and lateral margin

of the tonsil. A common pattern is three branches with an individual

branch being directed to the medial, intermediate, and lateral segments of

the suboccipital surface.

Vermian arteries

The vermian arteries usually arise from the medial trunk in the

vermohemispheric fissure. A common pattern is for there to be one or

two vermian branches. If two are present, they are often directed to the

median and paramedian segments. If no vermian branches are present, the

vermian area is usually supplied by the contralateral PICA.

Tonsillar branches

The tonsillar branches usually arise from the lateral trunk and most

commonly supply the medial, posterior, inferior, and part of the anterior

surfaces of the tonsil. If there are no branches directed predominantly to

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the tonsil, the tonsil is supplied by the adjacent hemispheric and vermian

branches.

Relationship to the cranial nerves

The PICA has the most complex relationship to the cranial nerves of any

artery (26, 33, 34). The vertebral artery courses anterior to

glossopharyngeal, vagus, accessory, and hypoglossal nerves, and the

proximal part of the PICA passes around or between and often stretches

or distorts the rootlets of these and adjacent nerves.

The inferior olive protrudes from the anterolateral surface of the medulla

near the vertebral artery and the origin of the PICA. The hypoglossal

nerve joins the brainstem on its anterior border and the glossopharyngeal,

vagus, and accessory nerves on its posterior border. Most PICAs arise at

the level of the olive, but some will arise rostral or caudal to that level.

The PICA origins at the level of the olive are either lateral or anterior to

the olive. The PICA origin is anterior to the olive if the vertebral artery

pursues its usual course anterior to the olive, but if the vertebral artery is

tortuous and kinked posteriorly, the PICA origin is lateral to the olive.

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Figure 5: Illustration showing the complex relationships of the rootlets of

the lower cranial nerves to the origin and initial segments of the right

PICA.

Hypoglossal rootlets

The hypoglossal nerve arises as a line of rootlets that exits the brainstem

along the anterior margin of the caudal two-thirds of the olive in the

preolivary sulcus, a groove between the olive and the medullary pyramid.

The hypoglossal rootlets, in their course from the preolivary sulcus to the

hypoglossal canal, pass posterior to the vertebral artery, except in the rare

instance in which they pass anterior to the artery. If the vertebral artery is

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elongated or tortuous and courses lateral to the olive, it stretches the

hypoglossal rootlets dorsally over its posterior surface.

The relation of the origin and proximal part of the PICA to the

hypoglossal rootlets varies markedly. The PICA arises either rostral or

caudal or at the level of the hypoglossal rootlets. The majority of the

PICAs arise at the level of the hypoglossal rootlets near the junction of

the hypoglossal rootlets with the medulla. The PICAs that arise superior

or inferior to the hypoglossal rootlets usually course superior or inferior

to, rather than between, the hypoglossal rootlets. The hypoglossal rootlets

are frequently stretched around the origin and initial segment of the

PICAs that arise at the level of the caudal two-thirds of the olive, in

addition to being stretched posteriorly by the vertebral artery. About half

of the PICA origins are located anterior to and half posterior to or at the

level of the rostrocaudal line drawn through the exits of the hypoglossal

rootlets from the medulla.

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Figure 6: The PICA loops upward before turning caudally and passing

between the rootlets of the vagus and accessory nerves. The hypoglossal

nerve arises from the brainstem in front of the olive. One of the rootlets

of the hypoglossal nerve loops upward around the origin of the PICA

before descending to join the other rootlets at the hypoglossal canal

The vertebral artery courses from the lateral side of the inferior part of the

medulla to the anterior surface of the superior part of the medulla. Those

PICAs arising inferior to the olive, arise posterior to the level of the

hypoglossal rootlets if the vertebral artery at the site of origin of the PICA

has not coursed far enough anterior to reach the level of the hypoglossal

rootlets. The PICA origin is anterior to the hypoglossal rootlets if the

vertebral artery, on reaching the hypoglossal rootlets, was anterior to the

olive. The PICA origin is located at the level of or posterior to the

hypoglossal rootlets if the vertebral artery at the site of origin of the PICA

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courses lateral to the olive and stretches the hypoglossal rootlets

posteriorly.

The initial segment of the PICA has a variable course in relation to the

hypoglossal rootlets. The most common course is for the PICA to arise

from the vertebral artery and pass directly posteriorly around or between

the hypoglossal rootlets. However, some PICAs will loop upward,

downward, or laterally in front of the hypoglossal rootlets before passing

posteriorly between or around them.

Glossopharyngeal, vagus, and accessory nerves

After coursing posterior to the hypoglossal rootlets, the PICA encounters

the rootlets of the glosso-pharyngeal, vagus, and accessory nerves. These

nerves arise as a line of rootlets, which then exit the brainstem along the

posterior edge of the olive in the retro-olivary sulcus, a shallow groove

between the olive and the posterolateral surface of the medulla.

The glossopharyngeal nerve arises as one or rarely two rootlets posterior

to the superior third of the olive, just inferior to the pontomedullary

junction and anterior to the foramen of Luschka and the rhomboid lip of

the lateral recess of the fourth ventricle. The vagus nerve arises inferior

to the glossopharyngeal nerve as a line of tightly packed rootlets posterior

to the superior third of the olive. The accessory nerve arises as a widely

31  

separated series of rootlets that originates from the medulla and upper

cervical cord, inferior to the vagus nerve below the level of the junction

of the upper and middle third of the olive. The glossopharyngeal and

vagus nerves arise rostral to the level of origin of the hypoglossal rootlets.

The accessory rootlets arise at both the level of and, inferior to the origin

of the hypoglossal rootlets.

The PICA commonly passes from the lateral to the posterior aspect of the

medulla by passing between the rootlets of the glossopharyngeal, vagus,

and accessory nerves. The PICA may be ascending, descending, or

passing laterally or medially or be involved in a complex loop that

stretches and distorts these nerves as it passes between them.

Facial and vestibulocochlear nerves

The facial and vestibulocochlear nerves arise superior to the

glossopharyngeal nerve at the level of the pontomedullary junction. The

proximal part of the PICA usually passes around the brainstem inferior to

the facial and vestibulocochlear nerves. However, in some

cerebellopontine angles, the proximal part of the PICA, after coursing

posterior to the level of the hypoglossal rootlets, loops superiorly toward,

even compressing, the facial and vestibulocochlear nerves before

descending to pass between the glosso-pharyngeal, vagus, and accessory

rootlets.

32  

Embryology of PICA:

The embryological vascular development shows that basilar and vertebral

arteries are formed from plexiform formations around the brainstem, with

transverse branches connected by longitudinal remnants of the prominent

lateral channel (41). The PICA also develops from these plexiform

formations, which may lead to many anatomic variations of the PICA.

Such developmental characteristics would act as an important congenital

factor for aneurysm formation at the straight portion of arteries. In other

words, there would be fragile points at the straight portion of the PICA.

Types of PICA aneurysms:

PICA aneurysms can be divided into three distinct forms depending upon

their morphology: saccular, fusiform, and dissecting (35). It is sometimes

difficult to differentiate among these three types of aneurysm

radiographically. Yamaura (35) in his series of 94 vertebral aneurysms

reported that 90 of the aneurysms were arising at the VA-PICA junction

or from the distal segment of PICA reported that among PICA

aneurysms 61.1% were saccular aneurysms, 10% were fusiform

aneurysms, and 28.8% were dissecting aneurysms.

33  

According to the location on the PICA they can be further characterised

as:

1) Junction PICA-VA aneurysms: usually arose at a curve where

the vertebral artery turned medially to join the contralateral

vertebral artery. Thus, they tended to arise just above the PICA

origin in the angle between the vertebral artery and PICA,

usually pointing superiorly and often partially embedded into the

anterolateral medulla (4).

2) Proximal segment aneurysms: those arising from anterior and

lateral medullary segments

3) Transitional segment aneurysms: those arising from

tonsillomedullary segment

4) Distal segment aneurysms: those arising from telovelotonsillar and

cortical segments

This is a surgical–anatomical classification schema, based on whether

the vessel lacks perforating vessels to the brainstem, is useful in

deciding whether the PICA can be potentially sacrificed at that point

without producing major functional impairment risks (36).

34  

Figure 7: Surgical–anatomical classification schema used to determine

the need for PICA preservation. Segments of PICA: green portion =

anterior medullary segment; orange portion = lateral medullary segment;

blue portion = tonsillomedullary segment; yellow portion =

telovelotonsillary segment; and red portion = cortical segment

Pathogenesis of PICA aneurysms:

These lesions followed the habit of aneurysms, set forth by Rhoton (13),

in that they occurred at branching points and at curves, and pointed

35  

in the direction that the blood flow would have taken if the curve had

not been present. Most of the evidence suggests that the predominant

contributor to their development is increased hemodynamic stress related

to hyperdynamic flow (37) and time (38, 39). When arising from small

peripheral vessels, particularly when associated with an AVM, these

lesions were often not associated with visible bifurcation sites, and the

length and pattern of the vessel wall that was affected resembled the

“side-wall blow out” often seen with dissecting aneurysms (36).

Although saccular intracranial aneurysms usually arise from the

bifurcation of arteries, distal PICA aneurysms occasionally have no

associated branching artery around the aneurysmal neck (4, 26, 40, 36).

Such branchless aneurysms can arise from a straight portion of the artery

in addition to a turning point (4, 10, 40). Hemodynamic stress and/or

congenital factors would be involved in the branchless aneurysm

formation at the distal PICA. The hemodynamic stress may cause

aneurysm formation at the hairpin curve of the PICA. Conversely, it is

not clear how the branchless aneurysm develops at the straight portion.

The PICA develops from the plexiform formations around the brainstem,

which may lead to many anatomic variations of the PICA (41). Such

developmental characteristics would act as an important congenital factor

36  

for aneurysm formation at the straight portion of arteries. In other words,

there would be fragile points at the straight portion of the PICA (42).

Stehbens (43) stated that large fusiform aneurysms are the direct result of

severe atherosclerosis with weakening of the wall. Rupture can occur but

is rare. Their pressure effects depend on size and anatomical

displacement associated with elongation and tortuosity of the parent

artery.

CLINICAL PRESENTATION:

The most common presentation in the published series

(4,42,2,44,45,46,8,9,47,36) was headaches, decreased level of

consciousness, and meningismus without focal deficits. Laine (48)

described a syndrome of localizing value for ruptured vertebral and PICA

aneurysms. However, in most cases, the symptoms of aneurysms at

this location are related to subarachnoid hemorrhage. Altough focal

neurological deficits are rare (40), these aneurysms can present as

bilateral abducent palsy, hemiparesis and truncal ataxia and this has been

described earlier (49, 20, 50). Even when these aneurysms reach giant

proportions, the clinical characteristics are quite variable, and these

lesions have been reported to present as posterior fossa tumor (51),

foramen magnum syndrome (50), obstructive hydrocephalus (52), and

cerebellopontine angle syndrome (53). Early evacuation of blood from

37  

the ruptured aneurysm at this location prevents severe neurological

impairment (54).

PATTERNS OF HEMORRHAGE:

The hemorrhage patterns shown on CT scans are generally specific to the

PICA segment from which the aneurysm arises. Blood in the fourth

ventricle without blood in the suprasellar, prepontine, and/or

circumesencephalic cisterns is said to be the typical CT appearance of

bleeding secondary to PICA-VA aneurysms (4). Some distal PICA

aneurysms present with only cerebellar or fourth ventricular hemorrhages

(55). Rupture of proximal PICA aneurysms is evidenced by presence of

clots within the ipsilateral basal cisterns, with or without extension into

the fourth ventricle. Isolated IVH without cisternal SAH is uncommonly

seen with proximal PICA aneurysms though more evident following

rupture of distal PICA aneurysms (4, 56, 55, 57). Aneurysms arising

from the tonsillomedullary segment are known to hemorrhage into the

fourth ventricle alone.

Rupture of aneurysms along the cortical or telovelotonsillar segment may

cause an intracerebellar hematoma that secondarily extends into the

ventricular system. Identification of any small focal peri-fourth

ventricular clot should alert the clinician to this possibility.

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39  

Therefore, a patient presenting with neither hydrocephalus nor IVH

would be highly unlikely to harbor a ruptured PICA aneurysm. The

presence of SAH along the convexity would further diminish the

likelihood of a ruptured PICA aneurysm. When encountering a pattern of

SAH highly atypical of ruptured PICA aneurysms, difficult vertebral

artery catheterizations might be deferred in the acute setting. Conversely,

encountering a pattern highly typical for ruptured PICA aneurysms would

mandate careful evaluation of the vertebral arteries, even if other

aneurysms had already been angiographically documented (56).

The possible patterns of bleeding due to other causes have to be

borne in mind. In nonhypertensive younger patients, vermian or

cerebellar hemisphere clots (often having extension into the ventricular

system) are most commonly caused by an underlying structural vascular

lesion such as an AVM. In contrast, hypertensive cerebellar hemorrhages

most commonly occur in men during their sixth through eighth decades,

originate in the dentate nucleus but may enlarge to involve the vermis

medially, and generally do not extend into the ventricular system unless

quite large (59, 60).

Most spontaneous IVH's result from rupture of a parenchymal

hematoma into the ventricles, but occasionally subarachnoid blood

refluxes into the ventricular system from the basal cisterns.

40  

Hypertensive hemorrhage is the most common source of spontaneous

IVH, but the condition was recognized less frequently prior to

development of CT imaging of the brain (61, 62, 63). In a report of 54

adult patients with IVH, 14 cases were due to rupture of saccular

aneurysms (62).

Compared with other intracranial aneurysms, ruptured PICA

aneurysms represent a unique subset of intracranial aneurysms with a

higher incidence of IVH and secondary hydrocephalus (56, 64). The high

frequency of IVH in ruptured PICA aneurysms may result from the close

association between the PICA and the foramina of Luschka and

Magendie, with retrograde flow of extravasated blood into the fourth

ventricle (58, 65). It is likely that the higher frequency of hydrocephalus

associated with PICA aneurysms compared with other aneurysms is

related to the high frequency of IVH in ruptured PICA aneurysms (56).

Early CT literature suggested that extensive supratentorial SAH

was unusual with ruptured posterior fossa aneurysms. More recent

literature has noted extensive supratentorial SAH in as many as 50% of

ruptured posterior fossa aneurysms (58). Kallmes et al. (56), reported that

supratentorial SAH was present in 70% of cases.

41  

ANGIOGRAPHIC FEATURES:

The digital subtraction angiography remains the "gold standard" in

preoperative neuroradiological imaging of aneurysms (2).

Figure 9: Antero-posterior view of a digital subtraction angiogram of a

patient with ruptured PICA aneurysm showing a small saccular aneurysm

arising at the VA-PICA junction.

The importance of performing a complete four-vessel angiogram in this

setting has been emphasized previously (66, 67). Although arteriography

of the dominant vertebral artery reveals the aneurysm, the necessity for

direct visualization of each VA and its PICA has been repeatedly stressed

42  

by many authors. One should not depend on washout down the

contralateral VA to provide adequate visualization of opposite PICA.

Less well appreciated is a curious lack of visualization of the aneurysm

by initial studies in this location; hence the need to repeat arteriography

until one is completely satisfied with the anatomical delineation (46). The

mechanism in this situation is unclear, and may involve the lysis of a clot

extending into the neck of the aneurysm (46). Hudgins et al. (4) and

Salcman et al. (46) reported two patients each whose PICA aneurysms

were missed on initial angiograms. Horiuchi et al. (42) in their study,

reported that the initial angiograms did not show a distal PICA aneurysm

in 5 (21.7%) of 23 patients.

It is also important to determine whether the PICA is reduplicated,

whether the opposite artery is present, whether the PICA territory is

irrigated by another vessel (e.g., the AICA), and whether the posterior

communicating arteries are present and, if so, whether they are

exceptionally large or fetal in nature; all of this information is vital in the

event of a planned or emergency vertebral occlusion (68, 69, 70).

Vasospasm (combined angiographic and clinical) was found in seven out

of 21 patients in the study by Hudgins et al. (4). This incidence of 33% is

essentially the same as that reported for all aneurysms (71). Gacs et al.

(45) reported 4 cases of vasospasm in their series and were of the opinion

43  

that spasm of the major arteries was found only after rupture of

aneurysms located on the more proximal segments of the cerebral

arteries. Bleeding of the more distal aneurysms caused no spasm or spasm

only in the neighboring small arteries. These findings may support the

debated role of local, direct, mechanically induced factors elicited by the

aneurysm rupture in the pathogenesis of spasm in SAH.

Figure 10: Lateral view of a digital subtraction angiogram of a patient

with ruptured PICA aneurysm showing a small saccular aneurysm arising

at from the caudal loop of the PICA (tonsilomedullary segment).

44  

Figure 11: Lateral view of a digital subtraction angiogram of a patient

with ruptured PICA aneurysm showing a small saccular aneurysm arising

at from the telovelotonsillar segment of PICA.

Aneurysm size is an important factor in determining hemorrhage risks

and treatment options, particularly in those patients presenting with

unruptured lesions. The “safe” size under which hemorrhage is less

probable is most often quoted as less than 10 mm (72, 73). This rule

clearly does not apply to distal PICA aneurysms. Small peripheral

aneurysms arising on the cerebellar arteries probably have thinner walls,

rendering them more prone to hemorrhage (45).

45  

The most important angiographic findings of dissecting aneurysms are:

irregular tapering or narrowing of the arterial lumen; intimal flap;

double lumen; false aneurysm; and irregularity of the arterial wall

with a wave-like pattern but no appreciable luminal narrowing. Among

such findings, confirmation of the true lumen and the false lumen is

the true "diagnostic sign."(74) It is very difficult to differentiate

fusiform aneurysms and dissecting aneurysms on the basis of VA

angiography alone.

The individual anatomy of the AICA and the PICA is quite variable.

They generally complement each other and the caliber of these two

vessels is often found to be inversely proportionate to one another. The

AICA-PICA variant is a well-recognized entity in which the AICA

provides blood supply to the distribution of both the AICA and the PICA.

This variant is relatively common seen in nearly 24% of routine vertebral

angiograms. The caudal trunk of AICA supplied the ipsilateral PICA

territory in 22% of cases.

46  

Figure 12: Preoperative CT angiogram (A, anteroposterior; B, oblique)

and vertebral angiogram (C, anteroposterior; D, lateral) showing

aneurysm from the tonsillar segment of left AICA-PICA variant. Post

operative angiogram (E, anteroposterior; F, lateral) demonstrating

complete obliteration of the aneurysm after clipping.

Association with AVMs:

In 2.7% to 8.7% of patients with AVM's intracranial aneurysm is a

simultaneous finding (75, 76, 77, 78). On the other hand, based on the

work of Locksley (1) and Suzuki and Onuma (78) only about 0.1%

of patients with aneurysms show simultaneous occurrence of AVM's.

The association of AVM's and aneurysms may be partly explained on

47  

the basis of a congenital vascular anomaly and partly by the

presumption that the increased blood flow through the feeding arteries

hemodynamically facilitates aneurysm formation. Because of the rate

of occurrence of aneurysms in the general population (5% in autopsy

cases (79, 80)), some authors believe that the 2.7% to 8.7%

simultaneous occurrence of aneurysm in AVM cases is probably

coincidental (81).

Authors of recent reports have suggested that the incidence of aneurysms

arising in association with AVMs may be as high as 46% (78, 82, 83, 84),

and that the incidence may be greater for infratentorial lesions (85). All

aneurysms associated with AVMs in a large number of series reported in

the literature were located on distal segments of the PICA, which fed the

AVM; a markedly increased incidence when compared with

supratentorial AVMs (82, 84). These aneurysms may not remain stable

and have been shown to be dynamic lesions that evolve over time (37,

86). Aneurysms arising near the nidus have been specifically identified as

potentially carrying an increased risk of hemorrhage (83, 87). Others,

however, report that the risk of hemorrhage is higher for the AVM (88).

48  

Treatment

Preoperative management

All patients are begun on oral Nimodipine 60mg 4th hourly upon

admission. Other standard procedures include bed rest in a quiet room,

blood pressure control if necessary, initiation of antiepileptic, analgesic

for headache and occasional use of phenobarbital for sedation.

Emergency ventriculostomy might be required in a patient with

hydrocephalus associated with depressed consciousness.

Surgical treatment

PICA-VA complex aneurysms

Surgery for aneurysms of the PICA-VA complex has traditionally been

carried out at a delay of several days to weeks (46). Yamaura (35) had no

examples operated on within 72 hours of the SAH, and only two

operations were performed at less than 1 week. All of the 21 cases in the

series reported by Hudgins and colleagues (4) were done on a delayed

basis, possibly due to referral pattern at their institution. Salcman et al.

(46) advocate early surgery when feasible, because relatively little

retraction is required for exposure and the structures involved (i.e., the

brainstem and cranial nerves) do not swell appreciably after hemorrhage,

unlike the cerebral hemispheres.

49  

The PICA has the most variable course of all the cerebellar arteries,

and its course is the primary determinant of the location of the

aneurysm and of the direction in which the aneurysm is pointing. The

point at which the aneurysm originates determines the surgical approach

and alternatives in aneurysm obliteration (4). Aneurysms at the PICA-

vertebral junction and the initial two segments of the PICA would

best be approached via an elongated suboccipital incision one finger’s

breadth mesial to the mastoid process and 10cm in length (46). Trapping

procedures should not be used on these aneurysms, as blood flow

to vital medullary perforators may be compromised.

The patient is placed in the lateral recumbent "park bench" position. This

approach appears advantageous in PICA-vertebral junction aneurysms

for several reasons (4) : 1) there is a decreased incidence of air embolism

and hypotension, because the head is lower than the heart; 2) less

retraction on the cerebellum (and if necessary, the medulla) is

necessary, as gravity causes them to fall away; and 3) the potential

obstructive effect of the jugular tubercle and foramen magnum can be

minimized by the superior and more lateral angle of this exposure.

A major cause of morbidity in PICA-vertebral aneurysms is the

inadvertent disruption of the rootlets of the ninth through the 12th

cranial nerves. The PICA takes a variable course through these

50  

rootlets, frequently looping superiorly so that it touches the anterior

or inferior surface of the facial and/or vestibulocochlear nerve (26).

With the patient in the "park bench" position, the rostral location of

the surgeon allows better visualization of proximal aneurysms in this

area, and minimizes the amount of retraction and dissection necessary

for excellent visualization and clip placement (4).

In most far lateral suboccipital craniectomies, it is not necessary to

remove the posterior lip of the foramen magnum or the arch of C1 (46,

89).

The majority of PICA aneurysms (76%) are located at or below the knee

of the vertebral artery, where it turns forward to run ventral to the brain

stem (4). The PICA arises dorsal or lateral to the aneurysm in almost

every case, with the exception of an occasional PICA posterior and

medial to the neck; hence, a lateral approach results in the vessel being

delineated before dissection of the aneurysm itself (90).

The clip is usually applied with the blades pointing forward, parallel to

the long axis of the VA distal to the PICA-VA junction (46).

51  

Figure 13: Illustration demonstrating surgical clipping of a right-sided

VA-PICA junction aneurysm. This can often be accomplished with a

straight clip; however, wide-neck aneurysms often require a straight

fenestrated clip placed down the long axis of the VA, including the PICA

origin in the fenestration as shown.

The extreme tortuosity of the vertebral and PICA arteries may also

occasionally influence the laterality of the operative approach. Drake (25)

described an aneurysm arising from the right vertebral artery distal to

the PICA which was clipped through a left suboccipital craniectomy

because the tortuosity of the vertebral artery caused it to cross the

52  

midline. In using the contralateral approach to a PICA aneurysm, the

vertebral artery on the side of the surgery should be traced to its junction

with the ipsilateral PICA without any initial regard for the contralateral

artery; since the origin of the opposite PICA is often at approximately the

same level, retraction of the brainstem can be carried out at this point if

necessary and the contralateral aneurysm identified (46).

Yamaura et al. (91) has correlated the risk of serious morbidity for all

PICA-VA complex aneurysms with a proximity to the midline of less

than 10mm; another unfavourble prognostic factor is a distance of more

than 13mm from the clivus to the aneurysm. In the latter circumstance,

the aneurysm is buried on the ventral aspect of the brainstem and

retraction of the medulla may be required to reach it.

Traditionally, a paramedian suboccipital craniotomy is used (92, 93).

Nevertheless, the closer the lesion is to the foramen magnum, or the

farther away it is toward the midline, the more difficult it is to visualize

adequately all the anatomical details of the region with the standard

approaches without extending the craniotomy at the skull base level. It is

now well known that both the far-lateral approach and the transcondylar

approach are very useful in treating VA–PICA aneurysms. (2,8,89,94).

Different terminologies are used to describe the far-lateral approach

described by Heros (89) to the VA and VBJ regions, depending on the

53  

extent of the bone removal. These terms include the lateral suboccipital,

posterior suboccipital, posterolateral, dorsolateral, far-lateral, extreme

lateral, transcondylar, supracondylar, paracondylar, and transcondylar

fossa approach (95, 96, 97, 89, 98). Thorough inferolateral bone removal

in the suboccipital region, accompanied by removal of the posterior arch

of C-1 laterally to the sulcus arteriosus of the vertebral artery, provides

excellent exposure of the vertebral artery throughout its intracranial

course to the vertebrobasilar junction with minimal or no retraction of the

medulla (89).

The patient is placed in the straight lateral position. The head is

maintained with the nose straight ahead (at a 90° angle from the floor)

and with a 30°-angle tilt toward the ipsilateral shoulder. The skin incision

is started at about the level of the top of the ear in a sagittal plane about

three finger-breadths medial to the mastoid. The incision first extends

straight downward toward the mastoid, then curves sharply medially to

the midline, and then goes straight downward to the spinous process of C-

2.

The craniectomy extends from the junction of the transverse and sigmoid

sinuses superolaterally to just beyond the midline through the foramen

magnum inferiorly in a teardrop fashion with the wider opening

superolaterally. The arch of C-1 is removed from just beyond the midline

54  

in the opposite side to the sulcus arteriosus underlying the vertebral

artery. Removing the arch of C-1 allows an approach from a more

inferior direction, below the cerebellar tonsil, without having to retract

the cerebellar hemisphere medially (89). The most important aspect of

this exposure is a very radical removal of bone in the area of the foramen

magnum going laterally as far as the condylar fossa, just posterior to the

occipital condyle and just above and behind where the vertebral artery

enters the dura (89). This extreme lateral removal of bone in the area of

the foramen magnum is the key to being able to approach the front of the

brain stem from an inferolateral angle with minimal or no brain-stem

retraction.

Aneurysms at a more distal PICA origin are usually approached in the

space between the 11th cranial nerve and the ninth and 10th cranial

nerves. The vertebrobasilar junction can usually be approached from

inferolaterally, still working between the 11th cranial nerve inferiorly and

the ninth and 10th cranial nerves superiorly, and following the vertebral

artery distally with the line of vision essentially in the same direction of

the artery.

When using lateral approaches, the jugular tubercle and the occipital

condyle are confronted as obstacles. The former constitutes a greater

problem in VA–PICA aneurysm surgery (98).

55  

Bertalanffy and Seeger (99) have described their transcondylar approach

for treating lesions in the lower clivus and the anterior portion of the

craniocervical junction. Their approach is very useful for treating lesions

located in the anterior portion of the foramen magnum. In the

transcondylar approach, the essential step is a partial resection of the

occipital condyle and lateral atlantal mass.

The transcondylar fossa (supracondylar transjugular tubercle) approach

described by Matsushima et al. (98) is an anatomically refined version of

the far-lateral approach described by Heros. In the transcondylar fossa

approach, the condylar fossa and the posterior portion of the jugular

tubercle are extradurally removed up to the hypoglossal canal by using

the posterior condylar canal and the emissary vein as anatomical

landmarks without injuring the atlantooccipital joint. The occipital

condyle is kept intact. The transcondylar fossa approach provides an

entire view of the cerebellomedullary cistern including the VA, the

anterior and lateral medullary segments of the PICA, the cisternal portion

of the ninth, 10th, 11th, and 12th cranial nerves, and the lateral recess in

the cerebellomedullary fissure.

56  

Distal PICA aneurysms

Because of the high incidence of bleeding when these aneurysms are

small, distal PICA aneurysms should be obliterated in almost all instances

whenever they are encountered (36).

Patients presenting with hemorrhage (real or suspected), in whom an

aneurysm is the only pathological condition identified, should be treated

urgently and not in a delayed fashion. Those patients presenting with

hemorrhage who harbor both an aneurysm and an AVM should also be

treated promptly. In this situation, the aneurysm is often the source of

bleeding, and the natural history of such lesions if untreated appears

much worse over a shorter interval than that of the AVM as a separate

entity (87, 100). A decision whether to treat the AVM at the same

hospitalization should be made, depending on the individual

characteristics of the AVM itself, particularly its size, location, and the

method chosen to obliterate the aneurysm.

The ideal treatment of a truly saccular lesion is clipping or endovascular

obliteration of the aneurysm neck with preservation of the lumen of the

PICA. A different strategy must be considered, however, whenever the

underlying cause of the lesion might represent a dissection (in which case

any residual vessel wall may be weakened and allow reformation of the

aneurysm) or when a seemingly saccular lesion cannot be clipped without

57  

parent vessel occlusion. In such cases, aneurysm location relative to the

origin of brainstem perforating vessels becomes the most crucial factor

when choosing a treatment option.

A surgical–anatomical classification schema (36), based on whether the

vessel lacks perforating vessels to the brainstem, is useful in deciding

whether the PICA can be potentially sacrificed at that point without

producing major functional impairment risks. If the PICA is sacrificed,

leptomeningeal communications with the superior cerebellar artery and

the AICA are usually sufficient to protect against functionally significant

cerebellar infarctions (37).

Direct inspection of the affected segment during open surgery provides

several significant advantages compared with endovascular therapy,

particularly in cases of proximal lesions (36). Direct visualization of the

affected arterial segment allows for better decisions regarding the need to

sacrifice or spare the parent vessel. Clips placed obliquely across the

PICA can be quite focally and accurately applied to spare the patency of

perforating vessels, whereas a longer segment of the PICA is often

sacrificed whenever the artery is obliterated by endovascular means.

Surgery is also preferable whenever a significant hematoma needs to be

evacuated, when a coexistent AVM is identified that can be

simultaneously removed with a low risk (particularly when the bleeding

58  

source is unclear), or when PICA preservation must be maintained (for

example, if the aneurysm is found in a proximal location or if there is a

dominant PICA with a very small AICA) (36).

For those lesions treated surgically, a combination of midline and lateral

suboccipital skull base approaches are useful, depending on the segment

of the PICA that is affected, the need for PICA reconstruction, and the

presence and location of an associated AVM.

For proximal lesions, a far-lateral suboccipital–transcondylar approach

provides sufficient proximal PICA exposure to ensure adequate

visualization and working room to apply temporary or permanent clips

and to perform direct anastomosis if required.

For aneurysms arising within transitional or distal segments, a bilateral

midline suboccipital craniotomy is usually sufficient, with additional

bone removal ipsilateral to the aneurysm or AVM and tonsillar

mobilization as needed.

For those aneurysms located beneath the tonsil, where mobilization of

this structure may be associated with a risk of premature rupture, subpial

tonsilar resection may be a preferred technique for exposure.

If an aneurysm, particularly a dissecting one, involves predominantly a

side-wall blow out, the apparently healthy residual portion of the vessel is

59  

often weak and aneurysm reformation can easily occur. For such lesions

in which PICA flow must be maintained, aneurysm ablation can be

achieved and the patency of the PICA lumen can be preserved by

stacking a row of fenestrated clips (36).

Whenever the safety of leaving a patent PICA is questioned, sacrifice of

the vessel should be seriously considered. In such circumstances,

excision of the aneurysm and arterial reconstitution, performed either by

direct end-to-end anastomosis or insertion of an interposed arterial graft

(most commonly taken from the OA) may be possible options. When

direct reconstruction is not possible, a clip placed on the PICA proximal

to the aneurysm (including the rupture site) combined with a PICA–PICA

or OA– PICA anastomosis are applicable solutions (36).

60  

Figure 14: Drawings depicting surgical strategies used to treat

“unclippable” distal PICA aneurysms. A: Fusiform distal PICA

aneurysm. B: Clip reconstruction achieved using stacked fenestrated

clips. C: Aneurysm resection and direct reanastomosis. D: Aneurysm

resection and interposed graft. E: Proximal ligation (flow reversal) and

distal bypass. F: Aneurysm trapping and distal bypass: G: Aneurysm

trapping and PICA–PICA anastomosis.

 

61  

AIM OF THE STUDY

The aim of this study was to retrospectively study the PICA aneurysms

treated surgically at our institute and to know the outcome of treatment.

62  

MATERIALS AND METHODS

All patients who were surgically treated at the Department of

Neurosurgery, Sree Chitra Tirunal Institute for Medical Sciences and

Technology, Thiruvananthapuram, with the diagnosis of PICA aneurysm

had their charts retrospectively reviewed for the period of January 1991

to June 2011.

Data were collected concerning patient age, sex, time interval between

date of ictus to date of admission, clinical symptoms and signs at the time

of ictus and at presentation, WFNS grade, computerized tomography

features including presence of subarachnoid hemorrhage [SAH],

intraventricular hemorrhage [IVH], intracerebellar hemorrhage [ICeH],

infarcts and hydrocephalus, angiographic features including aneurysm

characteristics (location on PICA, type and size), existence of multiple

aneurysms, timing of surgery, surgical approach and procedure, and

postoperative neurological complications.

Patient’s condition and outcome (Glasgow Outcome Scale [GOS]) were

evaluated at the time of discharge and at 6 and 12 months after discharge.

The clinical outcomes were categorized according to the Glasgow

Outcome Scale as favorable (good recovery and moderate disability) or

unfavorable (severe disability, vegetative state, or dead).

63  

RESULTS

Demographics:

During the study period between January, 1991 and June, 2011, twenty

eight patients with PICA aneurysms were treated surgically and formed

the basis for this series. The results of all the 28 patients are summarized

in Table 1. There were 21 females (75%) and 7 males (25%), with female

to male ratio of 3:1. The average age of the patients was 45.22 years, with

a range of 25 to 68 years. The mean time from ictus to referral was 12.82

days, with a range of 2 to 93 days.

Clinical characteristics:

Headache was present in all the patients (100%), altered sensorium was

present in 28.57% (n=8), and neck stiffness was present in 50% (n=14).

Four patients (14.28%) presented with cerebellar signs. Two patients

(7.14%) presented with lower cranial nerve palsy. Two patients (7.14%)

had a lateral rectus restriction, both on the side of the aneurysm. None of

the patients presented with limb weakness. WFNS grade was grade I in

85.71% patients (n=18), grade II in 14.28% patients (n=3). There were no

patients with a WFNS grade III or above. Six patients had a history of

hypertension and two patients had a history of chronic smoking.

64  

Case Age/ Sex

Presentation WFNS grade

CT findings

Side Site (segment)

Form Associated malformation

Surgery (approach/ procedure)

ETV/ VPS

Outcome (GOS)

1 41/M HA 1 SAH, IVH R 1(origin) Saccular none MS / clipping No 5

2 61/F HA, V 2 SAH, IVH, HCP

R 1(origin) Saccular none LS / clipping No 5

3 65/F HA, V - IVH L 1(origin) Saccular ACom aneurysm

LS / clipping No 5

4 49/F HA, LCN, CE - InCeH L 3 Saccular none LS / clipping No 5

5 52/F HA, V 1 SAH, IVH R 1(origin) Saccular none LS / clipping No 5

6 38/M HA, V, CE 1 SAH, IVH L 2 Saccular none LS / clipping No 5

7 38/F HA - IVH L 4 Saccular none MS / clipping No 5

8 45/M HA, V 1 SAH R 1(origin) Saccular none LS / clipping No 5

9 44/M HA, V 1 SAH, IVH L 4 Saccular none LS / clipping No 5

10 58/M HA, V 2 SAH, IVH, HCP

R 1(origin) Saccular Right SCA & MCA aneurysm

LS / clipping No 3

11 25/F HA, V 1 SAH, IVH R 1 Saccular none LS / clipping No 5

12 28/F HA, V 1 SAH, IVH, HCP

L 2 Saccular none LS / clipping No 5

13 56/M HA, V, LCN 1 SAH, IVH, HCP

L 1(origin) Saccular none LS / clipping No 5

14 35/F HA, CE 1 SAH, IVH R 4 Saccular none MS / clipping No 4

15 44/F HA, V 1 SAH, IVH R 1(origin) Saccular none LS / clipping Yes 1

16 66/F HA, V 1 SAH, IVH R 4 Saccular none MS / clipping No 5

17 35/F HA, V 1 SAH, IVH, HCP

L 1(origin) Saccular none LS / clipping No 5

18 38/F HA, V - IVH L 1(origin) Saccular none LS / clipping No 5

19 62/F HA 1 SAH,HCP L 1(origin) Saccular none LS / clipping No 5

20 34/F HA - InCeH L 4 Saccular none MS / clipping No 5

21 35/F HA, V, CE, LR

2 SAH, IVH, HCP

L 2 Fusi-saccular

none MS / aneurysmorraphy + wrapping

Yes 5

65  

Table 1: Clinical data of 28 patients with PICA aneurysms

ACoM, anterior communicating artery; CE, cerebellar signs; ETV, endoscopic third ventriculostomy; GOS, Glasgow outcome scale (at discharge); HA, headache; HCP, hydrocephalus; IVH, intraventricular hemorrhage; L, left; LCN, lower cranial nerve dysfunction; LR, lateral rectus paresis; LS, lateral suboccipital approach; MCA, middle cerebral artery; MS, midline or paramedian suboccipital approach; R, right; SAH, subarachnoid hemorrhage; SCA, superior cerebellar artery; V, vomiting; VPS, ventriculoperitoneal shunt, #: AICA-PICA variant aneurysm

Symptoms and signs Number of patients (percent) Headache 28 (100%) Neck stiffness 14 (50%) Altered sensorium 8 (28.57%) Lateral rectus paresis 2 (7.14%) Glossopharyngeal & vagal palsy 2 (7.14%) Cerebellar signs 4 (14.28%)

Table 2: Presenting symptoms and signs

22 49/F HA, V 1 SAH,HCP InCeH,

L 1 Saccular none LS / aneurysmorraphy

Yes 5

23 45/F HA, V 1 SAH, IVH, HCP

L 1(origin) Fusi-saccular

none LS / aneurysmorraphy

No 5

24 68/F HA, V - IVH, HCP R 4 # Saccular none MS / clipping No 2

25 42/M HA 1 SAH, IVH L 1(origin) Saccular none LS / clipping No 5

26 63/F HA, V 1 SAH, IVH L 3 # Saccular none LS / clipping No 5

27 33/F HA, V - IVH, HCP L 3 Saccular none MS / clipping No 5

28 62/F HA, V 1 SAH, IVH R 1(origin) Saccular none LS / clipping No 5

66  

Figure 15: Pie chart showing the skewed sex ratio of PICA aneurysms in

this study

Computerized tomography features:

All the patients who presented with acute symptoms consistent with SAH

underwent CT scanning within 24 to 48 hours after the ictus. In most of

the cases patients were referred to us after imaging from local hospitals

and there was a delay in patient referral. On examining their CT scans,

SAH was present in 75% (n=21) patients. Intraventricular hemorrhage

was evident in 82.14% (n=23) of the patients. Five patients (17.85%)

presented only with IVH. Intracerebellar hemorrhage (10.71%) was

observed in the vermis of 1 patient and in the hemisphere of 2 others.

25%

75%

Sex ratioMale Female

67  

Twenty six patients (92.85%) had a Fisher (101) grade of 4 and two

patients (7.1%) had a Fisher grade of 3. Eighteen (64.28%) patients

demonstrated SAH with extension into the ventricular system. Isolated

IVH without cisternal SAH was seen with proximal PICA aneurysms in

10.52% (n=2), though it was more evident following rupture of distal

PICA aneurysms, 33.33% (n=3). Early hydrocephalus was present in

39.28% (n=11) of which 7.14% (n=2) of patients required an external

ventricular drain prior to surgery. Only one patient (3.57%) had a

cerebellar infarct.

Features on CT Number PercentSubarachnoid hemorrhage (SAH) 21 75% Intraventricular hemorrhage (IVH) 23 82.14% Intracerebellar hemorrhage (ICeH) 3 10.71% Isolated IVH without SAH 5 17.85% Hydrocephalus (HCP) 11 39.28% Infarct 1 3.57%

Table 3: Computerized tomography features

Angiographic features:

Four-vessel cerebral angiography was done in all the patients. In 26

(92.85%) patients the angiogram revealed the aneurysm while in the

remaining 2 patients, a second angiogram repeated after 2 weeks detected

the aneurysm.

68  

Fifty percent (n=14) patients had aneurysms located at the PICA origin.

Rest of the aneurysms were located along the PICA, with 7.14% (n=2)

arising from the anterior medullary segment, 10.71% (n=3) from the

lateral medullary segment, 10.71% (n=3) from the tonsillomedullary

segment, 21.42% (n=6) from the telovelotonsillar segment and none from

the cortical segment. Nineteen aneurysms (67.85%) were located on the

proximal segment of PICA and 32.14% (n=9) were located on the distal

segment. We had two cases of distal AICA-PICA variant aneurysms, one

arising from the telovelotonsillar segment and the other from the

tonsillomedullary segment.

Location of aneurysm Number Percent VA-PICA junction 14 50% Anterior medullary segment 2 7.14% Lateral medullary segment 3 10.71% Tonsillo-medullary segment 3 10.71% Telovelotonsillar segment 6 21.42% Cortical segment 0 0% Right side 11 39.28% Left side 17 60.71%

Table 4: Location of PICA aneurysms on angiography

Among the treated aneurysms 26 (92.85%) were saccular in shape and 2

(7.14%) were fusi-saccular arising from the PICA proper. Of the 28 PICA

aneurysms, 23 (82.14%) were small (<1.5cm) in size, 4 (14.28%) were

69  

large (1.5 – 2.5cm) and one (3.57%) was a giant aneurysm (>2.5cm). Of

the 28 PICA aneurysms 39.28% (n=11) were located on the right and

60.71% (n=17) on the left. 89.28% (n = 25) of the patients treated had

only one aneurysm, whereas 7.14% (n = 2) had multiple aneurysms.

Associated vascular anomalies were noted in two cases. One had an

aneurysm arising from the ACom artery and the other patient had two

aneurysms, one arising from the ipsilateral SCA and the other from

MCA. Angiographic evidence of vasospasm was not found in any patient.

Preoperative care:

All patients were begun on oral Nimodipine 60mg 4th hourly upon arrival

at our institution. Other standard procedures consisted of bed rest in a

quiet room, blood pressure control if necessary, initiation of antiepileptic

(phenytoin), paracetamol for headache and occasional use of

phenobarbital for sedation. No patient had recurrent hemorrhage after

arrival at our institution.

Surgical procedure:

Of the 28 ruptured aneurysms, none were treated within 48 hours of

hemorrhage, 35.71% (n=10) were treated within 2 to 5 days, and 64.28%

(n=18) were treated after a time period longer than 5 days. The reason for

late treatment was generally delayed referral. No patient had recurrent

70  

hemorrhage upon arrival at our institution. All proximal aneurysm

clippings were performed using a lateral, suboccipital approach and those

in the distal segments were approached using a midline/ paramedian

approach. Twenty five aneurysms (89.28%) were directly clipped without

any intraoperative complications. One patient (Patient no: 21) had a large

fusi-saccular aneurysm from the lateral medullary segment that was

partially thrombosed and calcified. Aneurysmorrhaphy was done with

prolene suture and wrapped with muscle tissue. In 2 patients (patient no:

22 and 23) in view of poor aneurysm configuration for clipping,

aneurysmorrhaphy was done with multiple clips. None of the cases

required parent vessel occlusion or bypass procedure. Intraoperative

temporary arterial occlusion was performed depending on the surgeon

and the extent of aneurysm dissection. It never exceeded 3 minutes

without at least a 5 minute period of reperfusion. There was no

intraoperative complication of aneurysm rupture. Estimated blood loss

was 500ml or less for all procedures.

Two patients had multiple aneurysms. The patient who had an anterior

communicating artery aneurysm (Patient no.3) underwent pterional

craniotomy and clipping of the aneurysm during the same admission. The

post-operative period was uneventful. The patient who had a right

superior cerebellar artery and middle cerebral artery aneurysms (Patient

71  

no.10) had a poor outcome after surgical clipping of PICA aneurysm that

had bled. The patient developed transient lower cranial nerve palsy and

required tracheostomy. He was discharged to a local hospice for nursing

care and was lost to follow-up.

Complications and outcomes:

Six of the patients (21.42%) developed new postoperative neurological

deficits representing neurological complications. Three (10.71%) patients

developed vocal cord paralysis, two of them requiring tracheostomy; one

being transient in nature. Three (10.71%) patients underwent CSF

diversion in the form of a ventriculoperitoneal shunt or endoscopic third

ventriculostomy for persisting radiographic hydrocephalus. Three

(10.71%) developed postoperative gait ataxia which improved in one

patient but persisted to a mild degree in 2 patients at 1 year follow-up.

Postoperative CT image in both these patients revealed a small ipsilateral

cerebellar infarct without any mass effect. One patient (3.5%) died

during hospitalization, and no patient subsequently hemorrhaged. The

mean duration of hospital stay was 18.53 days (range 9 to 101 days). 25

patients were discharged home, 2 were transferred to a rehabilitation

facility and 1 died in the hospital.

When analyzed according to aneurysm size, 21.73% (n = 5) of the

patients with lesions less than 1.5 cm in diameter developed at least one

72  

new postoperative neurological complication each, whereas 25% (n = 1)

of the patients with aneurysms that were 1.5 to 2.5 cm in diameter did so,

and the one patient with aneurysm that was larger than 2.5 cm in diameter

did not develop any new deficits. The patients with distal aneurysms had

a 33.3% (n = 3) incidence of ataxia after surgery.

A check conventional angiogram / CT angiogram after surgery was

performed in 16 (57.14%) patients depending on the surgeon’s

preference. None of the angiograms revealed any residual aneurysm.

Patient’s status at discharge and at follow up was recorded using the

Glasgow Outcome Scale (GOS, Table 5). GOS scores were determined at

the time of discharge for 100% of the patients (n=28), at 6 months after

discharge for 25 patients (89.28%) and at 1-year after discharge from the

hospital for 20 patients (71.42%). At 6 months follow-up, 24 (85.71%)

patients were independent (GOS score of 4 or 5) and had a favourable

outcome and at 1 year after discharge, 20 (71.4%) patients who continued

to be on regular visits were independent. The reduction in percent at 6

months and at 1 year was because of a reduction in the number of patients

available for follow up.

When the outcome was analyzed according to the location of the

aneurysm, 17 proximal PICA aneurysms (89.4%) had a favourable

outcome (GOS score of 5 or 4); whereas 2 proximal PICA aneurysms

73  

(10.52%) had an unfavourable outcome (GOS of 3, 2 or 1). Seven distal

segment aneurysms (77.77%) had a favourable outcome (GOS score of 5

or 4); whereas 2 distal PICA aneurysms (22.22%) had an unfavourable

outcome (GOS of 3, 2 or 1).

Score

Outcome

1 Dead

2 Vegetative state

3 Severe disability; able to follow commands/unable to live independently

4 Moderate disability; able to live independently, unable to return to work or school

5 Good recovery; able to return to work or school

Table 5: Glasgow Outcome Scale, scale for measurement of outcome after brain injury (102) Glasgow outcome scale score Number (%) 5 24 (85.71%) 4 1 (3.57%) 3 1 (3.57%) 2 1 (3.57%) 1 1 (3.57%)

Table 6: Glasgow outcome scale score for 28 patients who underwent surgical treatment for PICA aneurysms

74  

Figure 16: Surgical outcome for 28 patients with ruptured PICA aneurysms, favourable outcome (GOS of 5 or 4), unfavourable outcome (GOS 3, 2 or 1)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

5

10

15

20

25

30

Favourable unfavourable

Outcome

75  

 

DISCUSSION

DEMOGRAPHICS:

Between January, 1991 and June, 2011, 28 cases of PICA-vertebral

and distal PICA aneurysms were operated upon in the Neurosurgery

Department at SCTIMST.

There was a striking female predominance (75%, n=21). Several other

series of PICA aneurysms demonstrate a similar female predisposition (4,

42, 2, 44, 45, 46, 8), while the series by Dimsdale and Logue (103) and

Lewis et al. (36) show an equal male to female ratio. Only the series of

Hammon and Kempe (104) shows a male predominance, a skew not

unexpected from their predominantly military population at Walter

Reed General Hospital, USA.

In our study the average age of these patients was 45.22 years, with a

range of 25 to 68 years. The mean age of patients who present with PICA

aneurysms is younger than those with aneurysms at other locations.

Horiuchi et al. (42) reported a mean age of 62 years in their study of

distal PICA aneurysms. Hudgins et al (4) reported a mean age of 52

years. Lewis et al. (36) reported a mean age of 51 years. In a report by

Dernbach and colleagues (105), the mean age was slightly lower at 44.7

76  

years but with a similar sex distribution. The Hammon and Kempe series

(104) differs in that the average age of patients with PICA aneurysms is

33 years, and probably reflects their specialized referral base.

CLINICAL CHARACTERISTICS:

The mean time from ictus to referral was 12.82 days in our study. This

delay in referral skews our series toward patients who did relatively well

after their initial hemorrhage, and prevents any conclusions regarding the

natural history and preoperative mortality rate associated with such

lesions.

All patients presented with aneurysmal rupture. The most common

presentation in our series, as well as in others (4,42,2,44,45,46,8,9,47,36)

was headaches, decreased level of consciousness, and meningismus

without focal deficits. All patients presented with classic SAH symptoms:

sudden severe headache (usually occipital). This was followed by an

altered level of consciousness, in 8 cases. Five patients also had neck

pain. Thirteen patients had neck stiffness. Six patients had papilledema.

Twenty patients exhibited no focal abnormalities during the initial

evaluation. The remaining patients exhibited some focal neurological

deficits.

77  

Four patients in our series presented with cerebellar signs, predominantly

gait ataxia, attributable to unilateral cerebellar dysfunction caused by the

pressure effect of the aneurysm or the intracerebellar hemorrhage.

Although Laine (48) described a syndrome of localizing value for

ruptured vertebral and PICA aneurysms, this was not confirmed in our

series. However, in most cases, the symptoms of aneurysms at this

location are related to subarachnoid hemorrhage. Altough focal

neurological deficits are rare (40), these aneurysms can present as

bilateral abducent palsy, hemiparesis and truncal ataxia and this has been

described earlier (49, 20, 50). Even when these aneurysms reach giant

proportions, the clinical characteristics are quite variable, and these

lesions have been reported to present as posterior fossa tumor (51),

foramen magnum syndrome (50), obstructive hydrocephalus (52), and

cerebellopontine angle syndrome (53). Early evacuation of blood from

the ruptured aneurysm at this location prevents severe neurological

impairment (54). It is known that giant aneurysms of the distal PICA

are often present in patients with symptoms of extra or intra-axial

posterior fossa tumors or fourth ventricular tumors

(105,50,106,107,51).

The arachnoid trabeculae of the cisterna magna are coarse, and the only

structure surrounding the PICA is the network of caudal cranial nerves on

78  

the lateral medullary segment. In the event of aneurysm rupture, blood

can penetrate the ventricles without difficulty, allowing massive

bleeding and rebleeding (9).

Like patients who rebled from aneurysms at other sites, those with

ruptured distal PICA aneurysms display progressive disturbance of

consciousness. Also, with distal PICA aneurysm, respiratory

insufficiency is more likely to develop, and to be fatal, as a result

of rebleeding. Awareness of the higher risk of rebleeding with distal

PICA aneurysms is an important factor in their management (9).

However, no patient in our series presented with a rebleed or

hemorrhaged during the time interval between admission and surgery.

Patients presenting with SAH (n = 21) were stratified according to the

WFNS grading scheme (108). Without adjusting for other medical

illnesses, 85.71% (n=18) of the patients presented with WFNS grade 1,

14.28% (n=3) with grade 2 and none with grade 3 or above. Horiuchi et

al. (42) reported that poor preoperative grade adversely affected the

outcome of patients with distal PICA aneurysms.

PATTERNS OF HEMORRHAGE:

The hemorrhage patterns shown on CT scans are generally specific to the

PICA segment from which the aneurysm arises. Blood in the fourth

79  

ventricle without blood in the suprasellar, prepontine, and/or

circumesencephalic cisterns is said to be the typical CT appearance of

bleeding secondary to PICA-VA aneurysms (4). Some distal PICA

aneurysms present with only cerebellar or fourth ventricular hemorrhages

(55). Rupture of proximal PICA aneurysms is evidenced by presence of

clots within the ipsilateral basal cisterns, with or without extension into

the fourth ventricle. In our series, SAH was present in 75% (n=21)

patients, IVH was present in 82.14% (n=23) patients, intraparenchymal

hemorrhage was seen in 10.71% (n=3) patients. Eighteen (64.28%)

patients demonstrated SAH with extension into the ventricular system.

Isolated IVH without cisternal SAH is uncommonly seen with proximal

PICA aneurysms (10.52% (n=2) in our series) though more evident

following rupture of distal PICA aneurysms (33.33% (n=3) in our series)

(4, 56, 55, 57). Hydrocephalus was present in 39.28% (n=11) patients,

which was less compared to other series (56). Aneurysms arising from the

tonsillomedullary segment are known to hemorrhage into the fourth

ventricle alone.

Rupture of aneurysms along the cortical or telovelotonsillar

segment may cause an intracerebellar hematoma that secondarily extends

into the ventricular system. Identification of any small focal peri-fourth

ventricular clot should alert the clinician to this possibility. In our series

80  

intracerebellar hematoma was seen in 3 patients (10.71%) of which one

was due to a giant aneurysm from the proximal segment (Patient no.22).

Kallmes et al. (56) described the patterns of hemorrhage in 44

cases of angiographicaly confirmed ruptured PICA aneurysms. Posterior

fossa SAH was present in 95% of cases. Isolated posterior fossa SAH was

present in 30% of cases, but in no case was isolated supratentorial SAH

present. Supratentorial SAH was present in 70% of cases. Intraventricular

hemorrhage (IVH) with or without associated SAH was seen in 95% of

cases, whereas isolated IVH was seen in 5% of cases. Hydrocephalus was

present in 95% of cases. Both IVH and hydrocephalus were present in

93% of cases. Other authors also have noted high frequencies of IVH

associated with ruptured PICA aneurysms. Sadato et al. (58) detected

IVH in 13 (100%) of 13 cases of ruptured PICA aneurysms and Andoh et

al. (47) found IVH in 83% of cases.

Therefore, a patient presenting with neither hydrocephalus nor IVH

would be highly unlikely to harbor a ruptured PICA aneurysm. The

presence of SAH along the convexity would further diminish the

likelihood of a ruptured PICA aneurysm. When encountering a pattern of

SAH highly atypical of ruptured PICA aneurysms, difficult vertebral

artery catheterizations might be deferred in the acute setting. Conversely,

encountering a pattern highly typical for ruptured PICA aneurysms would

81  

mandate careful evaluation of the vertebral arteries, even if other

aneurysms had already been angiographically documented (56).

The high frequency of IVH in ruptured PICA aneurysms may

result from the close association between the PICA and the foramina of

Luschka and Magendie, with retrograde flow of extravasated blood into

the fourth ventricle (58, 65). It is likely that the higher frequency of

hydrocephalus associated with PICA aneurysms compared with other

aneurysms is related to the high frequency of IVH in ruptured PICA

aneurysms (56).

Early CT literature suggested that extensive supratentorial SAH

was unusual with ruptured posterior fossa aneurysms. More recent

literature has noted extensive supratentorial SAH in as many as 50% of

ruptured posterior fossa aneurysms (58). Kallmes et al. (56) reported that

supratentorial SAH was present in 70% of cases.

Angiographic features:

Although arteriography of the dominant vertebral artery reveals the

aneurysm, the necessity for direct visualization of each VA and its PICA

has been repeatedly stressed by many authors. One should not depend on

washout down the contralateral VA to provide adequate visualization of

opposite PICA. Less well appreciated is a curious lack of visualization of

82  

the aneurysm by initial studies in this location; hence the need to repeat

arteriography until one is completely satisfied with the anatomical

delineation (46). The mechanism in this situation is unclear, and may

involve the lysis of a clot extending into the neck of the aneurysm (46).

Two of the aneurysms in our series were invisible on the original study

despite a complete absence of vasospasm. Hudgins et al. (4), Salcman et

al. (46) also reported two patients each whose PICA aneurysms were

missed on initial angiograms. Horiuchi et al. (42) in their study, reported

that the initial angiograms did not show a distal PICA aneurysm in 5

(21.7%) of 23 patients.

It is also important to determine whether the PICA is reduplicated,

whether the opposite artery is present, whether the PICA territory is

irrigated by another vessel (e.g., the AICA), and whether the posterior

communicating arteries are present and, if so, whether they are

exceptionally large or fetal in nature; all of this information is vital in the

event of a planned or emergency vertebral occlusion (68, 69, 70).

We did not find any case with evidence of vasospasm in our series.

Vasospasm (combined angiographic and clinical) was found in seven out

of 21 patients in the study by Hudgins et al. (4). This incidence of 33% is

essentially the same as that reported for all aneurysms (71). Gacs et al.

(45) reported 4 cases of vasospasm in their series and were of the opinion

83  

that spasm of the major arteries was found only after rupture of

aneurysms located on the more proximal segments of the cerebral

arteries. Bleeding of the more distal aneurysms caused no spasm or spasm

only in the neighboring small arteries. These findings may support the

debated role of local, direct, mechanically induced factors elicited by the

aneurysm rupture in the pathogenesis of spasm in SAH.

In our series 39.28% (n=11) of the aneurysms were located on the right

and 60.71% (n=17) on the left. This finding may be related to the fact that

the left vertebral artery is the dominant or larger artery (69). The left

dominance of the

aneurysm may be caused by more hemodynamic stress than on the right

side.

Aneurysm characteristics:

In our series, 23 aneurysms were small in size, 4 were large and one was

a giant aneurysm. This is consistent with Drake's observation (25) that

most of these aneurysms are less than 1.25 cm or greater than 2.5 cm. We

did not, however, see the large percentage of giant aneurysms

reported by Drake (25,109) (six of 50 aneurysms) and Kempe (110)

(fifteen of 48 aneurysms). Even when these aneurysms reach giant

proportions, the clinical characteristics are quite variable, and these

84  

lesions have been reported to present as posterior fossa tumor (51),

foramen magnum syndrome (50), obstructive hydrocephalus, (52) and

cerebellopontine angle syndrome(53). Aneurysm size is an important

factor in determining hemorrhage risks and treatment options, particularly

in those patients presenting with unruptured lesions. The “safe” size

under which hemorrhage is less probable is most often quoted as less than

10 mm (72, 73). This rule clearly does not apply to distal PICA

aneurysms. Small peripheral aneurysms arising on the cerebellar arteries

probably have thinner walls, rendering them more prone to hemorrhage

(45).

In this study aneurysms are defined as saccular (26 cases) or fusisaccular

(2 cases), a decision based on the appearance of the lesion’s luminal

shape on arteriography and modified by surgical findings. Most fusiform

lesions represent dissecting arteries, although the classic arteriographic

features of pearl-and-string sign (15), a double lumen (74), linear defects,

and focal outpouching (14, 111) are difficult to demonstrate when

encountered in small vessels (for example, those on the peripheral PICA).

Although the finding of small peripheral aneurysms should prompt

consideration of infectious causes, no such lesions were encountered in

our series and are rarely described in the literature (112).

85  

Surgical treatment, complications and outcome:

In this series, 14 cases of VA-PICA aneurysms, 3 cases of proximal

segment aneurysms and 3 cases of distal segment aneurysms were treated

with a lateral suboccipital approach. Midline suboccipital approach was

used in 6 cases of distal segment aneurysms, one case of proximal

segment aneurysm, and one case of aneurysm arising at VA-PICA

junction.

The point at which the aneurysm originates determines the surgical

approach and alternatives in aneurysm obliteration. Aneurysms at the

PICA-vertebral junction and the initial two segments of the PICA

would best be approached via a lateral suboccipital approach to afford

the best visualization of their necks. Trapping procedures should not

be used on these aneurysms, as blood flow to vital medullary

perforators may be compromised. Aneurysms from the first two

segments of the PICA are best approached via a lateral exposure, but

those arising from the distal three segments, posterior to the brain stem,

are better handled through a bilateral (midline) suboccipital

craniectomy. The extreme tortuosity of the vertebral and PICA arteries

may also occasionally influence the laterality of the operative approach.

Although clipping across the aneurysmal neck is preferable, trapping

may be utilized in those lesions arising from or distal to the

86  

telovelotonsillar segment, as no further brain-stem perforators arise

beyond this point.

Only 21.42% (n=6) of the patients had new postoperative neurological

deficits, of which the majority recovered within 6 months. Nevertheless

7.14% (n=2) had persistent problems in the form of mild gait ataxia at 1

year after discharge. In our series postoperative morbidity was more

related to hydrocephalus than lower cranial nerve dysfunction. Of the

series that discuss perioperative morbidity, the incidence of transient and

permanent lower cranial nerve deficits ranges from 20% to 66%.

Favourable outcome (GOS of 5 or 4, good recovery or moderate

disability, respectively) was seen in 25 (89.28%) of the patients.

Unfavourable outcome (GOS of 3, 2 or 1, severe disability, vegetative

state, or dead respectively) was seen in 3 (10.71%) patients. A correlation

between the severity of the WFNS grades at the time of admission with

the GOS scores at the time of discharge could not be demonstrated

because of the small numbers and patient referral from local hospitals

after improvement in the neurological status.

Three patients had poor results. One of these patients (Patient no. 10) had

a small cerebellar infarct in the post-operative scan and transient lower

cranial palsy necessitating tracheostomy. He developed ventilator

associated pneumonia that was managed aggressively with intravenous

87  

broad-spectrum antibiotics and chest physiotherapy. He was discharged

to a local hospice after closing the tracheostomy, for general nursing care.

The second patient (Patient no 24), operated for a distal AICA-PICA

variant aneurysm was stable in the immediate postoperative period but

gradually deteriorated from the second day onwards. She developed

hemodynamic instability and irregular respiration, suggesting medullary

dysfunction. This was further complicated by neurogenic pulmonary

edema and fulminant meningitis. The patient underwent tracheostomy

and was kept on prolonged ventilator support. Serial postoperative CT

scans were normal. A postoperative vertebral angiogram was not done in

view of her poor neurological status and unstable hemodynamic

parameters. She had a stormy postoperative course and at the time of

discharge to another nursing care centre she was in a vegetative state.

Both the above mentioned patients never returned for follow-up visits.

The third patient (Patient no.15) underwent a ventriculoperitoneal shunt

for persistent hydrocephalus 2 days after clipping of PICA aneurysm. A

week after surgery she complained of chest pain following which she had

a cardiac arrest and could not be resuscitated. This was the only mortality

in our series that could not be directly attributable to the primary

pathology or its management.

88  

The experience of Charles G Drake and S J Peerless with 1767

vertebrobasilar artery aneurysms is the largest till date (92). Out of these

176 aneurysms were located at the VA-PICA junction (150) or on the

PICA (26). Twenty two of these aneurysms were giant (>25mm) in size.

Majority of the giant aneurysms had mass effect only, with various

degrees of bulbar paresis and ataxia, often with mild hemiparesis,

hemisensory loss, and limb dysmetria. VIth nerve palsy was the most

frequent preoperative cranial nerve dysfunction. In 75%, it recovered

completely. In 221 patients with vertebral or PICA aneurysms, more than

one-fifth of the patients had IX–X nerve deficits after surgery; two-thirds

of them were transient, but in follow-up, four patients had severe

dysphagia requiring prolonged tracheostomy. Intraoperative aneurysm

rupture (7%) was rare but dangerous: of 16 patients, 4 died and 1 was

severely disabled. They categorized outcomes as excellent, good, poor

and dead. Patients with good Hunt and Hess grades at the time of

admission had better overall outcome than patients who were in poor

neurological status. 94% of the patients with small aneurysms had good

results.

Yasargil (93) described 15 PICA aneurysms, 10 of which were at the

vessel origin. No specifics relating to outcome were provided aside from

noting that 14 patients had good outcomes and 1 had a fair outcome.

89  

R. J. Hudgins, et al. (4) in their experience with 21 surgically treated

PICA aneurysms. Forty-three percent were Hunt and Hess Grade I, 38%

were Grade II, and 19% were Grade III. Patients presenting with higher

grades had a greater incidence of adverse outcomes. Sixty-six percent of

Grade I patients were normal at the time of discharge, whereas only 25%

of Grade II and 50% of Grade III patients were without deficits. The

overall results included a 14% incidence of hydrocephalus, 14%

hemiparesis (10% postoperative hemiparesis), 33% dysarthria, 5%

dysphagia, 5% Wallenberg's syndrome, and 10% death. They divided

results into four categories: 1) good, able to return to full previous

activities; 2) fair, minor neurological deficits which slightly modified life-

style (such as functionally significant dysarthria, decreased palatal

excursion); 3) poor, disabling neurological deficits; and 4) death. In terms

of outcome, 62% of the patients returned to all previous activities, 19%

had minor new deficits that modified their previous lifestyles, 9.5% had

disabling deficits, and 9.5% died. This study, however, did not provide

specifics in terms of resolution of various symptoms during the

convalescent period.

Gacs et al. (45) reported their series of 16 peripheral aneurysms of

cerebellar arteries, out of which 8 had aneurysms of the PICA. They

noted vasospasm in the basilar and the vertebral arteries in 4 cases (all

90  

had a PICA aneurysm). Among the patients with PICA aneurysms,

outcome was excellent in 4 (50%), good in 2 (25%), poor in one and one

patient died.

Yamaura (35) reported 90 PICA aneurysms, 77 of which involved the

PICA origin. No specific data were provided concerning morbidity and

mortality, except the statement that three patients developed Cranial

Nerve VI palsy and eight patients developed Cranial Nerve IX and X

palsies. The authors' long-term results were truly remarkable. All lower

cranial nerve deficits improved in days to weeks, except in one patient,

who had a persistent hoarse voice after surgery.

Salcman et al. (46) studied 22 PICA aneurysms, 18 of which were at the

PICA origin, 4 were on the distal PICA. Out of these 17 were treated by

them. Three patients did not undergo surgery. Eighteen percent were

Hunt and Hess Grade I, 23.5% were Grade II, 41% were Grade III, 12%

were Grade IV and one was Grade V. Perioperative morbidity was seen

in 7% of the patients. They categorized outcomes as independent,

dependent and dead. Outcome included 64.7% patients who were

independent, 11.7% patients who were dependent and 23.5% were dead.

Their immediate perioperative morbidity and management mortality may

reflect the fact that the majority of their patients had aneurysms in Hunt

91  

and Hess Grades 3 and 4, a factor associated with higher morbidity and

mortality independent of the location of the aneurysm (113).

Yamamoto et al. (44) reported that the outcome for surgically treated

patients is generally favorable. In 42 (91 %) of the 46 surgical cases they

reviewed, the outcomes were good or excellent and only four patients

(9%) died.

Bertanalffy et al. (2) studied 27 patients with VA-PICA complex

aneurysms. Twenty-two patients in this series suffered from a

subarachnoid hemorrhage (SAH). Of these, two patients were admitted in

Hunt and Hess (H&H) grade I, two patients in grade II, 11 patients in

grade III, four patients in grade IV, and three individuals in grade V.

Aneurysms of the VA and the proximal PICA were approached via a

transcondylar (n=11) or lateral suboccipital route (n=3), while aneurysms

originating from the distal PICA were exposed via a paramedian

suboccipital craniotomy (n=7). Four of the patients treated surgically

required a permanent shunting due to a posthemorrhagic hydrocephalus.

Two patients developed a complete dorsolateral medullary syndrome due

to a partial occlusion of the PICA following prolonged intraoperative

temporary clipping of this vessel. Two patients had a transient sixth

cranial nerve palsy, two patients who had developed aspiration

pneumonia required prolonged ventilation. Two of the patients treated

92  

with surgery died postoperatively due to massive vasospasm.

Endovascular therapy was used in three patients who could not be treated

surgically. Twenty two (81.48%) patients had an excellent outcome, and

two (7.4%) patients had a fair outcome. These authors emphasize that

removal of the arch of C1 and partial drilling of the occipital condyle

provide an optimal view for proximal PICA aneurysms and minimize the

potential for injury to lower cranial nerves and perforating arteries in this

area. Their results are more promising with transient lower cranial nerve

palsies in only two patients (29%), neither of whom required

tracheostomy (0%), and CSF leak requiring a second operation in one

patient (14%).

Horowitz et al. (8) reported their surgical results for 38 patients with

PICA aneurysms. Their study clearly indicated that these lesions were not

benign and that overall outcome was good, with 91% of the patients

evaluated at 6 months after discharge being independent. Although 66%

of the patients had new postoperative neurological deficits, the vast

majority achieved significant recoveries. Nevertheless, 37% had

persistent problems at 1 year after discharge. 74% of the patients had a

GOS score of 1 or 2 at the time of discharge, 91% at 6 months after

surgery and 89% at 1 year after surgery. Higher GOS scores at the time of

discharge and at 6 and 12 months after discharge seemed to be associated

93  

with the presence of hydrocephalus and clinical vasospasm. Because of

the relatively small number of lesions within this study, they could detect

no firm correlations between Fisher grade and outcome. The severity of

the Hunt and Hess grades at the time of admission seemed to correlate

with the GOS scores at the time of discharge and at 6 months after

discharge, although statistical significance could not be demonstrated

because of small numbers and incomplete follow-up. Their opinion was

that by removing the ring of C1 and working more along the axis of the

brain stem with the operative side down in a caudal-to-rostral direction,

PICA aneurysms could be approached from the ventral side of the nerves,

thus reducing the need for excessive cranial nerve manipulation.

Lee et al. (114) described 14 PICA aneurysms, 10 of which were located

at the vessel origin. Outcomes for all 14 lesions were listed and included

29% vasospasm, 14% hydrocephalus, 14% dysphagia, and 7% vocal cord

paralysis requiring a tracheostomy. Of those patients presenting with

Hunt and Hess Grade I, all returned to full activity. Of those patients

presenting with Hunt and Hess Grade II, 66% returned to full activity and

33% died. Thirty-three percent of Hunt and Hess Grade III patients

returned to full activity, whereas 33% had poor outcomes and 33% died.

All Grade IV patients returned to full activity.

94  

S. B. Lewis, et al. (36) analyzed 20 consecutive patients with 22

aneurysms of the peripheral PICA. Sixty percent of the patients (12 of 20)

experienced some consequences of their disease and/or complications

during the course of their treatment, including hydrocephalus requiring

shunt placement (nine cases), ataxia (five cases), dysphagia (two cases),

pneumonia (two cases), hyponatremia (two cases), meningitis (one case),

repeated hemorrhage before treatment (one case), and Terson syndrome

(one case). Eighty percent of patients (16 in all) were functionally

independent (excellent, good, or fair) at the time of discharge from the

hospital. At the last follow-up examination, an excellent or good outcome

had been achieved in 17 (85%) of 20. Two patients had poor long-term

results and one patient died. Only one patient experienced a true lower

cranial nerve paresis related to surgical intervention. The distal nature of

aneurysms encountered in this series placed the majority of distal PICA

lesions superficial to the lower cranial nerves.

Horiuchi et al. (42) reported a series of 24 patients with 27 distal PICA

aneurysms. They found that unfavorable outcome was significantly

associated with the preoperative World Federation of Neurosurgical

Societies grade and the presence of obstructive hydrocephalus. They

further concluded that surgical outcome of PICA aneurysms located at the

proximal side of the PICA origin, especially the vertebral artery-PICA

95  

bifurcation, tends to be unfavorable compared with the distal PICA

aneurysm because of the deep, narrow operative fields, perforating

arteries to the brainstem, and the cranial nerves. In addition, size of the

aneurysm and Fisher group usually will have an impact on prognosis. The

most common site of the aneurysms was at the telovelotonsillar segment

(29.6%).

D’Ambrosio et al. (97) reported the clinical outcomes obtained via a far

lateral suboccipital approach in 20 consecutive proximal PICA

aneurysms. The far lateral suboccipital approach achieved adequate

exposure in all cases. There were no intraoperative complications or

intraoperative aneurysm ruptures. Two (10%) patients developed vocal

cord paralysis as a result of surgery, with only 1 (5%) requiring

temporary tracheostomy. There were three cases of CSF leakage

requiring wound revision, with one subsequent wound infection. Fourteen

patients (70%) had radiographic hydrocephalus, for which 8 (40%)

required external ventricular drain placement. Only 1 patient required a

permanent CSF diverting procedure in the form of a ventriculoperitoneal

shunt. One patient required tracheostomy and percutaneous endoscopic

gastrostomy for medical reasons unrelated to surgery. At 3 months of

follow-up, 93% of the subarachnoid hemorrhage patients achieved a

Glasgow Outcome Scale score of 1 to 2. At 12 months of follow-up, 92%

96  

achieved a Glasgow Outcome Scale score of 1 to 2. These authors

conclude that the far lateral suboccipital approach incorporating the

removal of the posterior arch of C1 can provide the added space

necessary to clip these lesions without undue manipulation of the lower

cranial nerves.

Al-khayat et al. (115) studied 52 patients to identify factors predicting

postperative lower cranial nerve palsy (LCNP) among patients

undergoing surgery for VA-PICA aneurysms. Postoperative LCNP

occurred in 25 patients (48.1%) with VA-PICA aneurysms. Of the factors

investigated, the use of temporary or total occlusion was associated with

increased incidence of postoperative LCNP. Nosocomial pneumonia

occurred only in patients with moderate to severe LCNP. Postoperative

LCNP resolved completely within 3 months in 12 patients (48%) and

within 6 months in 19 patients (76%).

97  

CONCLUSIONS

PICA aneurysms, by virtue of their relative rarity, strategic location and

complex anatomy pose unique diagnostic and technical challenges.

In treating patients with suspected SAH whose CT imaging is normal,

special attention should be given to the fourth ventricle and the possibility

of VA-PICA aneurysms.

Angiography should be performed with separate injections of each

vertebral artery. Occasionally, these aneurysms may be missed on the

initial study and therefore the study has to be repeated again after an

interval of at least 2 weeks. As compared with aneurysms at other sites,

PICA-VA lesions are frequently missed on the initial study and, on rare

occasions, must be looked for in extracranial locations.

Surgical planning must take into account the location of the aneurysm,

the presence of any anatomical variations of the parent vessel and the

need for an anastomosis or bypass procedure. Preoperative planning for

large PICA-VA aneurysms should include a contingency plan for

possible trapping or vertebral ligation. In this regard, preoperative test

occlusions of the vertebral artery with an intravascular balloon are

helpful.

98  

Although clipping across the aneurysmal neck is preferable, trapping

may be utilized in those lesions arising from or distal to the

telovelotonsillar segment, as no further brain-stem perforators arise

beyond this point. A thorough search for brainstem perforators is

essential prior to trapping though it has been claimed to be safe for

aneurysms arising distal to the choroidal point.

The use of a far lateral approach without condylar resection provides

sufficient space for aneurysm dissection without significant manipulation

of the lower cranial nerves, and avoids the increased morbidity associated

with condylar resection. Maintaining a caudal-rostral trajectory beneath

the cranial nerves rather than through them has significantly decreased

postoperative lower cranial nerve dysfunction that used to be the major

cause of morbidity.

Majority of PICA aneurysm patients have an excellent outcome after

surgical treatment and their presence should not deter the surgeon from

clipping them. Good results may be achieved in patients with PICA

aneurysms by tailoring the therapeutic strategy with consideration for the

condition of the patient, the arterial and aneurysmal morphology.

 

99  

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PROFORMA  

1. Name

2. Hospital number

3. Age/Sex

4. Date of ictus

5. Date of admission

6. Date of surgery

7. Date of discharge

8. Symptoms - Sudden onset headache / vomiting / LOC / others

9. History of hypertension / diabetes / chronic smoking

10. GCS, WFNS grade

11. Signs - Neck stiffness / Fundus / Lower cranial nerves / Other

cranial nerves / Cerebellar signs / motor weakness / others

12. CT Features – SAH location / intraventricular hemorrhage /

parenhymal hemorrhage / hydrocephalus / infarct / Fisher grade /

others

13. Pre-op EVD / ventilation / rebleed

14. DSA – location of aneurysm / type / size /evidence of rupture or

spasm / others

15. At surgery – approach / procedure / others

16. Post-op GCS, whether ventilated post-op (reason)

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17. Post-op CT head / post-op check angiogram

18. Post-op complications – cranial nerve palsy / weakness / cerebellar

signs / respiratory / others

19. Glasgow outcome scale score at discharge / at 3 months follow-up

/ at 6 months follow-up / at 1 year follow-up / at last follow-up

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ABBREVIATIONS

ACoM - anterior communicating artery

AICA – anterior inferior cerebellar artery

AVM – arteriovenous malformation

BA – basilar artery

CT – computerized tomography

CE - cerebellar signs

CSF – cerebrospinal fluid

DSA – digital subtraction angiogram

ETV - endoscopic third ventriculostomy

EVD – external ventricular drain

GCS – Glasgow coma scale

GOS - Glasgow outcome scale

HA – headache

HCP – hydrocephalus

ICeH - intracerebellar hemorrhage

IVH - intraventricular hemorrhage

LS - lateral suboccipital approach

LR - lateral rectus

LOC – loss of consciousness

LCN - lower cranial nerve

MCA - middle cerebral artery

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MS - midline or paramedian suboccipital approach

PICA - posterior inferior cerebellar artery

SAH – subarachnoid hemorrhage

SCA - superior cerebellar artery

VPS - ventriculoperitoneal shunt

VA – vertebral artery

V - vomiting

WFNS – World Federation of Neurosurgeons