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y
DR Mohammed
Riyas
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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
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Little things aboutCP angle
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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.
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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.
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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
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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
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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.
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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.
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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.
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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 .
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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 )
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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
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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.
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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.
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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
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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
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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.
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1. 2.
3.4.
INTRACANALICULAR CISTERNAL
COMPRESSIVE HYDROCEPHALIC
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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.
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Stage 1
Stage 2
Stage 3
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Cerebellopontine Angle:
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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.
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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
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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
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Symptoms & signs
Brainstem involvement:• There is ataxia, weakness and numbness of arms and legs
with exaggerated tendon reflexes.
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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
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Tumor Growth Rate
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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
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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
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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
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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
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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
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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.
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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.
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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.
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BERA patterns in AN
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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
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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
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MRI Brain
Isointense to brain,
hyperintense to CSF
Hyperintense to brain,
hypointense to CSF
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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.
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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.
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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.
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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
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Middle Fossa Approach.
Translabyrinthine Approach
Suboccipital Approach
Surgical Approaches
Factors that influence surgical approach selection
• Age
•Hearing status
•Tumour size
•Surgeon’s preference.
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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.
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Translabrynthine approach
◦ 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
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Translabrynthine approach
◦ 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
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Translabrynthine approach
◦ 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
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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.
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THANK YOU
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