vestibular schwannoma ... post graduate level

2.  Also known as acoustic neuroma ,
neurilemmoma or eigth nerve tumor
 Most common of all CP angle tumors
– 85% and constitutes around 6% of
all intracranial tumors.

4.  The CPA is a V shaped fissure formed by cerebellum wrapping
around the pons and medulla.
 Situated in lateral posterior fossa.
 Has superior and inferior limbs forming the margins of the angle.
 Sup and inf limbs meet laterally at the end of petrosal fissure.
 filled with CSF and contains tortous blood vessels and cranial
nerves .
 Inverted triangular shaped space

5.  CPA – Irregularly shaped potential space in the posterior fossa of
the brain .
 Anteriolaterally– posterior surface of temporal bone .
 Posteriomedially– anterior surface of the cerebellum and cisterns of
the pons & medulla and olive.
 Superiorly –cerebellar tentorium.
 Inferiorly – cerebellar tonsil.

9.  CSF
 Cranial nerves and their associated vessels
 Cerebellum flocculus
 Anterior inferior cerebellar artery
 Superior petrosal veins : at the upper edge of 5th cranial nerve.

10. Within the superior portion of cistern :5th nerve travels from lateral pons to
the meckel’s cave.
Within CPA: 7th and 8th nerve exits the brainstem at the pontomedullary
junction and enters porus acousticus.
Inferior portion of cistern: 9th,10th,11th nerves exit from medulla and enters
pars nervosa of jugular foramen.

11.  Encapsulated benign tumor arising from the
superior and inferior vestibular nerves.
 site of origin is debatable.
 Inf vestibular nerve> sup vest nerve (acc to
recent studies )
 Arise from schwann cells within the IAC –
lateral to Obesteiner redlich zone( glial
schwann cell junction) .

12.  Schwannomas rarely arise from the
cochlear nerve
 Schwannomas are rarely malignant.
 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

13.  Incidence – 1.9 tumors per 1 lakh people per year
 Types - Sporadic ( 95%) and non sporadic ( 5%)
 Age of presentation – 40 to 60 yrs. M:F=1:1
 Age of presentation is less in non sporadic ( 20-30 yrs )
 Mean growth rate – 1.1 mm /yr.

14.  Owing to mutations in the gene for the tumor suppressor protein
MERLIN /SCHWANNOMA located on chr 22q12.
 Merlin protein modulates cellular adhesion , proliferation and motility.

15.  Merlin acts on tyrosine kinase receptors and VEGF and its receptors.
 Anti VEGF drugs are under trial .
 VS may accelerate during pregnancy.

16.  GROSS :
 smooth surface with a yellow to gray color.
 usually solid , 5 to 20% cystic in nature and tend to have poorer
outcomes.
 MICROSCOPIC :
 Capsule – 3 to 5 micrometer in thickness.
 Two morphological tissue types – Antony A areas (elongated compact spindle
cells with rod shaped nuclei lying in rows) aka VEROCAY bodies
 Antoni B (looser stroma , fewer cells , myxoid change)
 Immunohistochemical stain : S 100 immunoperoxidase.

17. Develops in nerve sheath
Compresses rather than invading the nerve
Gradually fills all the IAC
Protrudes out of the porus acousticus
Resorption of bone surrounding the porus

18. Extrameatal 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

19. Tumor may extend 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.

20. 1. 2.
3.
4.
INTRACANALICULAR CISTERNAL
COMPRESSIVE HYDROCEPHALIC

21.  Vestibular schwannoma is a slow growing tumour.
 Occasionally tumor may undergo rapid expansion owing to
cystic degeneration or hemmorhage into the tumor.
 The initial intracanalicular growth affects the
vestibulocochlear nerve in the rigid IAC &
causes unilateral HL ,tinnitus and vertigo or dysequilibrium.

22. Stage 1
Stage 2
Stage 3

23. 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.

24.  Intracanalicular:
 Hearing loss (U/L progressive SNHL), tinnitus,
vertigo
 Level of hearing loss is not a predictor of tumor
size.
 b/l SNHL points towards NF2
 Cisternal:
 Worsened hearing and dysequilibrium
 Compressive:
 Cranial neuropathies
 CN V: Midface and corneal hypoesthesia
 CN VII : Hitzelberger’s sign( decreased sensation of
EAC),loss of taste and reduced lacrimation on
Schirmer’s test ,facial weakness ( late)
 CN VI : visual acquity and diplopia

25.  Hydrocephalic:
 Fourth ventricle compressed and obstructed
 Headache, visual changes, altered mental
status
 Nausea and vomiting
 On examination : ICP and papilloedema.
 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 towards affected side

26.  Brainstem involvement:
• There is ataxia, weakness and numbness of arms and legs
with exaggerated tendon reflexes.

27. STAGE TUMOUR SIZE
I (Small) <10mm
II(Medium) 11-25mm
III(Large) 25-40mm
IV(Giant) >40mm

28.  Majority present with complaints of U/L Hearing
Loss, Unilateral Tinnitus, Vertigo , dysequilibrium,
facial numbness , weakness or spasm.
 Initial step in evaluation includes an audiologic
assessment , if it suggests a retrocochlear lesion ,
then imaging of the CPA is performed .
 Vestibular testing lacks specificity in diagnosis of
VS

29.  PTA
 Speech discrimination score (SDS)
 Acoustic reflex threshold
 Acoustic reflex decay
 SISI score : 0-20%in 70-90%cases.
 ABR test
 PTA shows assymmetric , down sloping , high
frequency SNHL in almost 70% of patients

30.  Retrocochlear HL causes SDS to be lower than
predicted by the pure tone thresholds.
 Loss of acoustic reflex or acoustic reflex decay
is noted in most patients with VS

31.  In patients with VS , the ABR is partially or
completely 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.

32. audiological tests
Cochlear Retrocochlear
a) Pure tone audiometry Sensorineural hearing loss Sensorineural hearing loss
b) Speech discrimination
score
<90% Very poor
c) Roll over phenomenon Absent Present
d) Recruitment Present Absent
e) SISI Over 70% 0-20%
f) Threshold tone decay
test
<25db >25db
g) Stapedial reflex Present Absent
i) Stapedial reflex decay
test
Normal Present

33.  Not sensitive nor specific for diagnosing VS
 The MC test used is vestibulonystagmography
with caloric testing.
 The location of VS on the inf or sup Vestibular
N may also be predicted.

34.  Location of the tumor is predicted by
VEMP (vestibular evoked myogenic
potential)
 Inf vestibular nerve can be tested by
VEMP.
 pts with inf vestibular nerve tumor have
decreased or absent VEMP

36.  Introduction of CT in 1970 allowed axial
imaging with improved bone & soft tissue
evaluation.
 With the addition of iv iodinated contrast agent
,90 % of VS are enhanced further improving
diagnostic accuracy.

37.  Intracanalicular tumors & tumors extending
less than 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

38.  MRI :
 Gold standard for the diagnosis of vestibular
schwannoma.
 T1 weighted images shows hyperintense lesion
relative to CSF.
 T2 images show tumor as hypointense relative to CSF.
 Typically show ‘ice cream cone or mushroom ‘
appearance.
 CSF within the fundus of the IAC , lateral to the tumor is
known as “fundal cap”

39. Ice cream on cone
appearance

40.  Gadolinium based MRI is the
investigation of choice .
 Detects tumor as small as 1 to 2mm.
 T2 weighted fast spin echo techniques
are used as a screening tool in patients
with sensorineural hearing loss since it is
quicker and cost effective or for those
with contraindication to contrast
administration.

41.  OBSERVATION WITH SERIAL IMAGING
 STEREOTACTIC RADIATION
 MICROSURGERIES

42.  Patient’s preference
 Patient’s age and medical condition
 Size and the location of the tumor
 Auditory and vestibular function of
the tumor side and the contralateral
side.
 Tumor progression
 Surgeon’s preference

43.  Age >65years, preffered
 Patients with vestibular shwannoma in
the only hearing ear with serviceable
hearing and no imminent risk to
brainstem function.
 Tumour growth is monitored .
 VS has a growth rate of 0.25 to 3.2
mm/year whereas NF2 patients have
shown 1.3mm growth per year.
 Serial imaging at 6months interval is
done ,then yearly if no growth is seen.

44.  Advantage: no treatment may be
required if no growth is seen.
 Disadvantage: tumor may grow @25mm
per year hence this method having
inherent risk.

45. A high dose of radiation can be delivered
to a defined region, usually within a well-
immobilized system that conforms closely
to the 3D shape of the target volume.
 Various modalities are:
 Gamma knife
 LINEAC: linear accelerator photon
radiation therapy
 Proton beam therapy

47. Advantages:
 age >65 and patients with medical
conditions unfit for surgery are
benefitted.
 Early return to normal activity.
 Least risk of infection and csf leak as
compared to microsurgery.

48. Disadvantages:
Hearing loss may occur depending upon the
dose given to the cochlea. Should not ne
more than 6.9Gy
Hydrocephalus: due to proteinac debris
obstuction to the CSF flow.
Facial and trigeminal cranial neuropathies
Malignant transformation: 1:1000 over 5 to
30 years.

49.  Translabryinthine
 Middle cranial fossa approach
 Sub occipital (retro sigmoid)
approach
 Combined

50. Choice of the surgery depends upon
:
 Tumor size
 Tumor location
 Hearing function

51.  The appropriate approach for a particular pt. is
based on the hearing status , size of the tumor
, extent of IAC involvement and experience of
the surgeon
 The approaches are either hearing
preservative or ablating.
 The retrosigmoid & middle fossa approaches
are hearing preserving, while translabrynthine
approach is otherwise.

52.  The middle fossa approach is well suited for the
pts with good hearing and tumor<2cm.
 The retrosigmoid approach is well suited for those
with good hearing and tumor<4cm and not
involving the lateral part of IAC.
 The translabrynthine approach causes total
hearing loss and so is appropriate for the pts with
poor hearing(PTA>30dB) or pts with good hearing
and tumors not accessible by the hearing
preserving approach.

54.  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
 Under GA, with neurophysiological monitoring
long acting paralytic should be avoided to
monitor the integrity of facial nerve.
 Facial EMG monitoring is advised.
 Prophylactic dose of antibiotics and i/v dexa
before giving incision.

55.  AIM:to resect complete tumour with
preserving facial nerve and hearing
function if present pre operatively

56. Middle Fossa Approach.
Translabyrinthine Approach
Suboccipital Approach
Surgical Approaches
Factors that influence surgical approach selection
•Age
•Hearing status
•Tumour size
•Surgeon’s preference.

57.  The primary approach for removal of VS.
 Most direct route to the CPA & requires minimal
cerebellar retraction.
 Identification of facial n is possible.
 Surgeons can ensure complete removal
because fundus of IAC is widely exposed.
 Immediate repair of facial nerve is possible.
 Recovery is quite rapid with minimal pain and
excellent facial n results

58.  Obvious disadvantage is sacrifice of any
residual hearing.
 Technique :
 A postauricular incision is made 2 cm behind
sulcus
 Complete mastoidectomy is done,with identification
of the middle fossa dura, sigmoid sinus , LSSC ,
fossa incudis & facial n
 The sigmoid sinus is decompressed with a
diamond burr

59.  A labrynthectomy is begun by removal of bone in
the sinodural 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 and the subarcuate artery
 A bone is removed along the posterior fossa dura
medial to sigmoid sinus , the endolymphatic duct
and sac are encountered.

60.  Jugular bulb location is defined by locating
ampulla of posterior 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

61.  Once the medial portion of the IAC is exposed for 270
the 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 the
labrynthine portion of the facial n
 The posteroir fossa dura is opened inferior to and
parallel to the superior petrosal sinus over the
midportion of the IAC
0

62.  Using the bills bar as guide , and with a fine hook ,
the surgeon seperates the superior vest from facial
nerve.
 The capsule of the tumor is incised , & the tumor is
gutted with house urban dissector
0

64.  One of the possible routes of surgery for
hearing preservation.
 Good visualisation of the lateral extent of
the tumor.
 Posterior fossa access is limited.
 Max 1.5cm diameter of tumor can be
removed.

65.  6-7 cm curved incision starting at the
zygomatic arch just behind the pinna is
given

66.  Middle fossa craniectomy is done
Elevation of dura from anterior face of petrous pyramid proceeds
from posterior to anterior.
Eventual target is crest at the ridge of the petrous pyramid
(dashed line) and Porus acousticus (solid circle).

67.  IAC is identified by following methods:
Gspn is identified and tracing the gspn back
to geniculate ganglion ,follow the
labrythine segment of the nerve, iac is
located.
Sscc( arcuate eminence) is at an angle of
45 and 60 degrees to IAC

68.  Skeletonization of internal meatus
 Identification of 7th and 8th nerve.
 Removal of tumor
 closure

69.  Also known as suboccpital approach .
 For the removal of large tumors

70.  Curved incision 3cm behind the mastoid
process is made.

71.  Craniotomy is done 5x5cm, ant and
superior limits of bone removal being
sigmoid and transverse sinuses.
 Dural incision given
 Cerebellum retracted.
 Removal of tumor
 Closure.

72.  lntraoperative Complications :
1. Cranial Nerve Injury
2. Bleeding
3. Brain Edema
4. Venous Air Embolism
5. Cardiac Arrhythmias
6. Brain Herniation

73.  Postoperative Complications:
1. Hemorrhage
2. Infarction
3. Cerebrospinal Fluid Leak
4. Meningitis
5. Tension Pneumocephalus