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y

DR Mohammed

Riyas



INTRODUCTION

An acoustic neuroma (also called vestibular schwannoma)

is a benign tumor arising from abnormally proliferative

shwann cells , which envelope the lateral portion of the

vestibular nerve in the internal auditory meatus



Little things aboutCP angle



CP angle tumors

Represents 10 of all intracranial tumors.

Fatal without treatment.

VS account for 78 of CPA tumors - mostly from

vestibular branch of VIIIth Nerve.

Variety of other tumors arise from this area like

meningioma , CN swannomas , dermoid tumors , arachnoid

cysts ,lipomas , metastatic tumors , vascular tumors.



Anatomy of CP angle

CPA Irregularly shaped potential space in the posterior

fossa of the brain .

Anteriorly posterior surface of temporal bone .

Posteriorly anterior surface of the cerebellum.

Medially cisterns of the pons & medulla and olive.

Superiorly inferior border of pons & cerebellar peduncle.

Inferiorly cerebellar tonsil.







Anatomy of CP angle

CN s V ( superiorly ) , IX,X,XI (inferiorly ) transverse the

cephalic and caudal extent of the CPA.

The central structures crossing the CPA to & from the IAC

are CN VII & VIII s carrying with them a fine sheet of

arachnoid tissue upto IAC.

Schwann cells sorround these nerves beginning in the IAC ,

near the porus at the Obersteiner- Redlich zone.

Divisions of IAC



Anatomy of CP angle

CN s V ( superiorly ) , IX,X,XI (inferiorly ) transverse the

cephalic and caudal extent of the CPA.

The central structures crossing the CPA to & from the IAC

are CN VII & VIII s carrying with them a fine sheet of

arachnoid tissue upto IAC.

Schwann cells sorround these nerves beginning in the IAC ,

near the porus at the Obersteiner- Redlich zone.

Divisions of IAC



Anatomy of CP angle

AICA is the main artery in the CPA and is the

source of the labrynthine artery .

The labrynthine artery courses via the IAC & is

an end artery for the hearing and balance organs.



Vestibular schwannoma

Nerve sheath tumors of the superior and inferior

vestibular nerves.

They arise in the medial part of the IAC or the

lateral part of the CPA and cause clinical

symptoms by displacing , distorting or

compressing adjacent structures in the CPA.



Vestibular schwannoma

Mean incidence range 9.1 tmr/yr to 13 tmr/yr( as per SB)

0.7 to 1.2 VS per lakh population/yr ( ballenger )

Types - Sporadic ( 95 ) and non sporadic ( 5 )

Age of presentation 40 to 60 yrs.

Age of presentation is less in non sporadic ( 20-30 yrs )

Mean growth rate 1.1 mm /yr.



Tumor biology

Equal frequency in sup and inf vestibular ( but recent

japanese studies suggested 85 from inf vestibular )

Arise from schwann cells within the IAC lateral to O-R

zone in the area of scarpa ganglion.

Schwannomas rarely arise from the cochlear nerve & are

rarely malignant .



Tumor pathogenesis

Owing to mutations in the gene for the tumor suppresor

protein MERLIN located on chr 22q12.

Formation of VS requires mutation of both copies of the

merlin gene.

Somatic mutations in both copies of merlin gene results in

sporadic VSs .

Familial VS occuring in NF 2 requires only one somatic

mutation event .( inherit one )



Tumor pathogenesis

NF2 is autosomal recessive at gene level but inheritance is

autosomal dominant ( pseudodominant )

A mutation in the normal allele leads to bilateral VS by the age

of 20.

Genetic screens for the NF2 mutation have been developed and

are the basis for genetic counselling for family members of NF2

patients



Tumor pathogenesis

Biochemical factors- VS express neuregulin ,which controls

survival and proliferation of schwann cells and its receptors

erbB2 & erbB3.

FGF ,TGF B1 , PDGF & VEGF all these contribute to VS

proliferation.

VS may accelerate during pregnancy.



pathology

GROSS :

◦ VS have a smooth surface with a yellow to gray color.

◦Tumor is usually solid ,with occasional cystic components and therefore

has a firm to soft texture depending on solid to cystic components.

MICROSCOPIC :

◦Capsule 3 to 5 micrometer in thickness.

◦Two morphological tissue types Antony A & Antony B areas

◦VEROCAY bodies

◦VS sections stain S 100 immunoperoxidase.



T UMOR DEVELOPMENT

Develops in nerve sheath

Compresses rather than invading the nerve

Gradually fills all the IAC

Protrudes out of the porus

Resorption of bone sorrounding the porus



T UMOR DEVELOPMENT-extrameatally

xtrameatal expansion into the large & empty pontine cistern

Displacement and stretching of the VII & VIII th CN on the anterior

Compress cerebellum and trigeminal N

Compression & displacement of the brainstem & fourth ventricle

aspect of the tumor & of the AICA on the inferior aspect

(During this time IAM continues to become more & more widened )

which leads gradually to hydrocephalus



T UMOR DEVELOPMENT-extrameatally

umor may extent to the tentorium & can obstruct the

cochlear aqueduct

The AICA & lower cranial nerves are also displaced & become closely

Overtime , the trigeminal & abducens nerves become stretched

Adherent to the inf surface of tumor.

over the surface of the tumor and get thinned.



1. 2.

3.4.

INTRACANALICULAR CISTERNAL

COMPRESSIVE HYDROCEPHALIC



Tumor development…..

Periods of growth are intermixed b/w slow growth &

peroid of quescence.

Occasionally tumor may undergo rapid expansion owing to

cystic degeneration or hemmorhage into the tumor.

The initial intracanalicular growth effects the

vestibulocochlear nerve in the rigid IAC &

causes unilateral HL ,tinnitus and vertigo or dysequilibrium.





Stage 1

Stage 2

Stage 3





Cerebellopontine Angle:



Large Acoustic Neuroma: Tumors over 2.5 centimeters (this one is 2.6 cm) become impacted

into the brainstem and cerebellum. Complications associated with surgery and radiation are

higher. It is difficult to deliver an adequate dose of radiation to control tumor growth without

excessive dosing to the brainstem in tumors larger than this.





Symptoms & signs

Intracanalicular:

◦ Hearing loss (UL progressive ), tinnitus, vertigo

◦ Loss of speech discrimination out of propotion to HL

Cisternal:

◦ Worsened hearing and dysequilibrium

Compressive:

◦ Occasional occipital headache

◦ CN V: Midface, corneal hypesthesia

◦ CN VII : Hitzelberger’s sign, loss of taste and reduced

lacrimation on Schirmer’s test ,facial weakness ( late)

◦ CN II , IV , VI : visual acquity and diplopia



Symptoms & signs

Hydrocephalic:

◦ Fourth ventricle compressed and obstructed

◦ Headache, visual changes, altered mental status

◦ Nausea and vomiting

◦ On examination : ICP and pappiledema.

Compression of CN IX & X

◦ Dysphagia , aspiration and hoarseness

◦ Poor gag reflex and VC paralysis.

Cerebellar involvement( late )

◦ Incoordination , widely based gate , tendency to fall

owards affected side



Symptoms & signs

Brainstem involvement:• There is ataxia, weakness and numbness of arms and legs

with exaggerated tendon reflexes.



Jackler Staging System

STAGE TUMOUR SIZE

Intra canalicular Tumour confined to IAC

I (Small) <10mm

II(Medium) 11-25mm

III(Large) 25-40mm

IV(Giant) >40mm



Tumor Growth Rate



Duration of Symptoms Prior to

Diagnosis SYMPTOMS YEARS

Hearing loss 3.9

Vertigo 3.6

Tinnitus 3.4

Headache 2.2

Dysequilibrium 1.7

Trigeminal 0.9

Facial 0.6



Diagnostic evaluation

Average patient will require 4 years from theonset of symptoms to diagnosis.

Majority will present with complaints of UHL, UT,Vertigo , dysequilibrium, facial numbness ,weakness or spasm.

Initial step in evaluation includes an audiologicassessment .if it suggests a retrocochlear lesion ,

then imaging of the CPA is performed .

Vestibular testing lacks specificity in diagnosis of VS



AUDIOLOGICAL EVALUATION

Includes PTA , Speech discrimination score(SDS) , Acoustic reflex threshold & acoustic

reflex decay

PTA of patients with VS shows assymetric ,

down sloping , high frequency SNHL in almost

70% of patients



AUDIOLOGICAL EVALUATION

Retrocochlear HL causes SDS to be lower thanpredicted by the pure tone thresholds.

This out of propotion is furthur accenuatedwhen retested at a higher speech intensity

( roll over phenomenon )

Loss of acoustic reflex or acoustic reflex decay is

noted in most patients with VS



audiological tests

Cochlear Retrocochlear

a) Pure tone audiometry Sensorineural hearing loss Sensorineural hearing loss

b) Speech discriminationscore

<90% Very poor

c) Roll over phenomenon Absent Present

d) Recruitment Present Absent

e) SISI Over 70% 0-20%

f) Threshold tone decaytest

<25db >25db

g) Stapedial reflex Present Absent

i) Stapedial reflex decay

test

Normal Absent



VESTIBULAR TESTING

Not sensitive nor specific for diagnosing VS

The MC test used is ENG with caloric testing.

Shows reduced caloric response in the affected ear.

The extent of vestibular function present predicts theamount of post op vertigo.

The location of VS on the inf or sup Vestibular N mayalso be predicted.



AUDITORY BRAINSTEM RESPONSE

In patients with VS , the ABR is partially orcompletely absent , or there is a delay in

latency of wave V on the affected side.

An interaural delay of wave V greater than

0.2 ms is considered abnormal. ( 40-60 % )

Overall ABR has a sensitivity of > 90% &

specificity of > 90 % in detecting VS.



AUDITORY BRAINSTEM RESPONSE

In 20-30 % there are no identifiable

waveforms even with insignificant HL in

higher frequencies.

In 10-20 % only wave I is present.



BERA patterns in AN





Imaging studies

Intracanalicular tumors & tumors extending lessthan 5 mm into the CPA frequently are missed

with contrast enhanced CT.

Accuracy improved by air-contrast cisternography.

MRI was introduced in 1980 & has become the

GOLD standard for VS



Imaging studies MRI :

VII & VIII nerves as well as cerebellum ,brainstem , vasculature& other structures are well visualized on MRI

The addition of gadolinium furthur enhanced the diagnosticaccuracy

Typically a series of T1 weighed images in which CSF is darkand fat is bright, T1 with gadolinium contrast , T2 In whichCSF is bright is used.

A hypointense globular mass centered over the IAC on T1 With

enhancement on gadolinium.

VS are iso-to hypointense on T2.

T2 fast spin echo MRI without contrast as screening.

MRI B i



MRI Brain

Isointense to brain,

hyperintense to CSF

Hyperintense to brain,

hypointense to CSF



management options

The primary management of VSs is surgical removal.

Roles of observation and radiotherapy are currently for

the pts,who cannot tolerate a surgical procedure or have

a life span of < 5 yrs.

Surgical approaches to the CPA include:

◦

Translabrynthine◦ Retrosigmoid

◦ Middle fossa craniotomies.



management options

The appropriate approach for a particularpt. is based on the hearing status , size ofthe tumor , extent of IAC involvement andexperience of the surgeon

The approaches are either hearingpreservative or ablating.

The retrosigmoid & middle fossaapproaches are hearing preserving, whiletranslabrynthine approach is otherwise.



management options

The middle fossa approach is well suited for thepts with good hearing and tumor<2cm.

The retrosigmoid approach is well suited forthose with good hearing and tumor<4cm andnot involving the lateral part of IAC.

The translabrynthine approach causes total

hearing loss and so is appropriate for the pts withpoor hearing(PTA>30dB) or pts with goodhearing and tumors not accessible by the hearingpreserving approach.



management options

Three critical issues inherent to all the three techniques are:◦ Extent of exposure of IAC and CPA

◦ Identification and preservation of the facial nerve

◦ extent of brain retraction

These operations use electro physiologic

monitoring of CN VII and ABR in hearing

preserving approach.

S rgical Approaches

http://www.ganfyd.org/index.php?title=Image:Inside_base_of_skull.png



Middle Fossa Approach.

Translabyrinthine Approach

Suboccipital Approach

Surgical Approaches

Factors that influence surgical approach selection

• Age

•Hearing status

•Tumour size

•Surgeon’s preference.

http://www.ganfyd.org/index.php?title=Image:Inside_base_of_skull.png







Translabrynthine approach

◦ A labrynthectomy is begun by removal of bone in thesinodural angle along the horizontal scc

◦ Each SCC is then opened and followed into the vestibule,

with care taken to identify the ampulla of each SCC andthe subarcuate artery

◦ A bone is removed along the posterior fossa dura medial

to sigmoid sinus , the endolymphatic duct and sac areencountered.




◦ Jugular bulb location is defined by locating ampulla ofposterior canal. ( inferior extent of dissection )

◦ Bone is removed around the inferior aspect of IAC until

the cochlear aqueduct is identified

◦ Posterior aspect of the canal is skeletonized until the

superior edge of the internal canal is identified

◦ Bone is then carefully removed between th e middle

fossa dura & the IAC




◦ Once the medial portion of the IAC is exposed for 270the remaining piece of porus may be carefully removed

◦ Laterally the transverse crest should be identified at the

fundus of the IAC.

◦ Superiorly , the Bills Bar is identified together with thelabrynthine portion of the facial n

◦ The posteroir fossa dura is opened inferior to and parallelto the superior petrosal sinus over the midportion of the

IAC

0




◦ Using the bills bar as guide , and with a fine hook , thesurgeon seperates the superior vest n from facial nerve.

◦ The capsule of the tumor is incised , & the tumor is

gutted with house urban dissector

0





Radiotherapy :-

1. Conventional radiotherapy by external beam

has no role in the treatment of Acoustic Neuromas

due to low tolerance of CNS to radiation.

2 X – or Gamma knife surgery.



THANK YOU





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