Here is a presentation on vestibular schwannoma with emphasis on surgical anatomy and microsurgeries

1. Vestibular
Schwannoma
Presenter: Dr.Raja Preetham Betha

2.  Also known as acoustic neuroma, neurilemmoma or 8th Nerve tumour
 Most common of all CP angle tumours 85%
 And constitutes 6% of all intracranial tumours
 Encapsulated benign tumour arising from the Superior and inferior vestibular
nerves
 Inferior vestibular > Superior vestibular (recent studies)
 Tumour arises from Schwann cells within the IAC, lateral to Obersteiner
Redlich zone (glial schwann cell junction)
 Rarely malignant
 And bilateral in cases of Neuro fibromatosis Type-2
1

3.  Incidence- 23 tumours per million in a year (Ref Scott-brown 8th ed page 1232)
 Types- Solid and cystic
 Age of presentation- 40-60 yrs
 Male: female ratio- 1:1
 Mean growth rate- 1.1 mm/yr and faster in NF-2
 Genetics- due to mutation in gene for tumour suppressor protein
MERLIN/SCHWANNOMA located on chromosome 22q12
2

4. TUMOUR DEVELOPMENT
Develops in nerve sheath
Compresses rather than invading the nerve
Gradually fills the IAC
Protrudes out of porus acousticus
Resorption of bone surrounding the porus
3

5. TUMOUR DEVELOPMENT
Extrameatal expansion into the large & empty pontine cistern
Displacement and stretching of the VII & VIII cranial nerves
on the anterior aspect of tumour
Compresses cerebellum and Vth nerve
Compression and displacement of brainstem & 4th ventricle
Finally leading to hydrocephalus
4

6. 5

7. 6

8. Clinical features
 Intracanalicular:
- Hearing loss (U/L progressive SNHL), tinnitus, vertigo
- Bilateral SNHL points towards NF-2
 Cisternal:
- Worsened hearing and disequilibrium
7

9. Clinical features
 Compressive:
- Cranial neuropathies
- CN V: Midface and corneal hypoesthesia
- CN VII: Hitzelberger’s sign (decreased sensation of EAC), loss of taste, etc
- CN VI: visual acuity and diplopia
 Hydrocephalic:
- 4th ventricle is compressed and obstructed
- Headache, visual changes, altered mental status
- nausea, vomiting
- O/E: Raised ICP and papilloedema
8

10. Clinical features
 Compression on CN IX & X:
- Dysphagia, aspiration and hoarseness
- Poor gag reflex and vocal cord paralysis
 Cerebellar involvement:
- Incoordination and gait abnormalities
 Brainstem involvement:
- Ataxia, weakness and numbness of arms, legs with exaggerated
tendon reflexes.
9

11. Investigations:
1) PTA- shows asymmetric, sloping, high frequency hearing loss on 70% patients.
2) Speech discrimination score- thresholds are higher than PTA
3) Stapedial reflex- Threshold is greatly increased as in retrocochlear pathologies
Due to impaired conduction in cochlear nerve which may be
attributed to: demyelination, impaired blood supply
4) SISI: 0-20% in 70-90% of cases
5) BERA: Prolonged wave V or absolute latency
Interaural delay of >0.2 sec is considered abnormal (40-60% patients)
6) VEMP: very specific for inferior vestibular nerve tumours, they have decreased
or absent VEMP
10

12. 11
(a)T2-weighted axial MRI
(b) T1-weighted gadolinium-enhanced axial MRI showing a 6.6-cm solid and cystic VS
(c) Computed tomography showing the normal porus on the right side (single arrow),
with an enlarged and destroyed porus on the left side (double arrows).

13. Wait and Scan policy (Ref Scott-brown 8th ed page 1236)
 unilateral VS smaller than 15–20 mm extrameatal:
 yearly MRI for 5 years, followed by MRI every other year for 4 years, followed
by MRI after 5 years, after which the observation is terminated, if no growth
occurs.
 If significant growth occurs (0.25-3.2 mm/year), active treatment (surgery
or radiotherapy) is recommended.
 Primary treatment of tumours larger than 15–20 mm is recommended, as
further growth extends the tumour diameter into the range associated with a
considerable increase in treatment comorbidity (e.g. damage to the facial
nerve function).
12

14. What is Cerebello-
Potine angle?
13

15.  It is an inverted triangular space formed by cerebellum wrapping around the
pons and medulla
 Situated in lateral posterior fossa
 Filled with CSF and contains tortuous blood vessels and cranial nerves
 Anteriolaterally- posterior surface of temporal lobe
 Posteriomedially- Anterior surface of the cerebellum and cisterns of pons
and medulla
 Superiorly- Cerebellar tentorium
 Inferiorly- Cerebellar tonsil and IX,X,XI as they enter jugular foramen
and XII nerve
14

16. 15
Anteriolaterally- posterior surface of
temporal lobe
Posteriomedially- Anterior surface of
the cerebellum and cisterns of pons
and medulla
Superiorly- Cerebellar tentorium
Inferiorly- Cerebellar tonsil and IX,X,XI
as they enter jugular foramen and XII
nerve

17. The Internal Acoustic Meatus (IAM)
Parts:
 Porus or Inlet
 Canal proper
 Fundus laterally: Superior half Anterior: facial nerve
Posterior: Superior vestibular nerve
Inferior half Anterior: Tractus spiralis foraminosa
Posterior: Inferior vestibular nerve
16

18. 17

19. 18

20. 20

21. 20

22. 1.Translabrinthine 2. Middle cranial fossa 3. Retrosigmoid
Microsurgical approaches
21

23. Indications
1. Translabrinthine
 Tumour size > 2cm
 All tumours in CP angle
 Poor hearing
 Facial nerve
compressing VS
 Facial neuromas
2. Middle cranial fossa
 Intracanalicular VS or
<5mm extension into
CP angle
 Good hearing
 Younger age group
 Good facial nerve
function
3. Retrosigmoid
 Tumours having with
large extrameatal
component in posterior
fossa
 Good/ normal hearing
 Older age group
22

24. 1. Translabrinthine approach
The key steps in the operation are:
1. Skin and periosteal flaps
2. Extended cortical mastoidectomy
3. Bony labyrinthectomy
4. Skeletonization of the IAM
5. Dural Incision and Draining of Cerebrospinal Fluid.
6. Removal of tumour using standard neurosurgical techniques
7. Closure with obliteration of the middle ear and petrosectomy defect, usually with
abdominal fat.
23

25. Skin and periosteal flaps
 A large postaural C-shaped incision is
performed about 4 cm behind the
postaural groove
 The superiorly based flap has the
advantage that, if necessary, it can easily
be extended upwards to allow access to
the middle cranial fossa.
24

26. Extended Cortical Mastoidectomy
 The antrum is opened and the semicircular canals
are delineated.
 The mastoid (vertical) segment of fallopian canal
is skeletonized avoiding the exposure of the facial
nerve
 A forward lying sigmoid sinus is depressed by
creating a Bill’s island over it.
 Use of bipolar cautery on the surface of the
sigmoid sinus helps to shrink the lateral bulge of
sigmoid sinus.
25

27. Labyrinthectomy
 The labyrinthectomy is performed by drilling
over the posterior, lateral and superior
semicircular canals in the mentioned
sequence.
 Care is taken to preserve the most anterior
lip of the ampullary end of the lateral and
superior semicircular canals for preservation
of the tympanic and labyrinthine segments
of the facial nerve, respectively.
26

28. Exposure of Internal Auditory Meatus
 The middle fossa dura and presigmoid posterior fossa dura
are compressed
 The dome of the jugular bulb is identified but thin bone is
left over it.
 The bone medial to the vestibule is drilled to delineate the
internal auditory meatus.
 An inferior gutter (trough) is created by drilling between
the region of the inferior lip of the IAM and the jugular
bulb going towards the petrous apex.
 Similarly, a superior gutter is created by drilling between
the superior lip of IAM and the middle fossa dura towards
the petrous apex.
 This constitutes drilling 270° around IAM
 Now the thin shell of bone covering the internal auditory
meatus is removed to expose the dura of the meatus
27

29. Dural Incision and Draining of
Cerebrospinal Fluid
 The dura of the internal auditory meatus (IAM) is
incised between the superior and inferior vestibular
nerves.
 The presigmoid posterior fossa dura is bipolarized
and incised. This exposes the tumor.
 Draining the CSF helps to sink the cerebellum, and
takes it out of the field of surgery, thereby offering a
good view of the tumor in the cerebellopontine
angle without any cerebellar retraction.
28

30. Tumor Removal with Preservation
of Facial Nerve
 The arachnoid, covering the tumor in the cerebellopontine
angle, is separated from the tumor capsule.
 The tumor capsule is incised open and the contents are
debulked without any traction on the capsule.
 Dissection that is confined to the inside of the tumour should
be safe.
 If the inside tumour is very soft it is possible to reduce the
volume quite rapidly with suction alone.
 More solid tumours may require the use of the cavitational
ultrasonic surgical aspirator (CUSA)
 The capsule is then gently dissected off the neurovascular
structures and brainstem by remaining in the tumor capsule—
arachnoid plane to complete the tumor removal along with its
capsule.
 The facial and cochlear nerves are visualized intact after
tumor removal
29

31. Closure
 The aditus is sealed with fat, bone dust and bone
wax
 The cavity is sealed with long strips of fat which
extend from the mastoid cavity to the
cerebellopontine angle
 Care must be taken that the fat does not prolapse
completely into the cerebellopontine angle.
 The cavity is overstuffed with fat.
 The musculoperiosteal flaps are closed in airtight
fashion
 The subcutaneous and skin layers are closed
Separately.
 Tight mastoid bandage is applied.
30

32. preoperative MRI postoperative MRI
31

33. 2. Middle cranial fossa approach
The key steps in the operation are:
1. Skin and soft tissue incisions
2. Middle fossa craniectomy
3. Extradural approach to upper surface of temporal bone and to posterior fossa
4. Skeletonization of internal meatus
5. Identification of facial and vestibular nerves
6. Removal of tumour
7. Closure
32

34. 33
Incision begins in the pretragal area
and extends 7 to 8 cm superiorly, in
a gently curving fashion.
Two thirds of the craniotomy
window is located anterior
to the external auditory canal
(EAC).
The temporal lobe is supported by
the House-Urban retractor.

35. 34

36. 35

37. 36

38. 37
 The geniculate ganglion is found by
following the superficial petrosal
nerve posteriorly.
 Bill’s bar separates the facial nerve
from the superior vestibular nerve at
the lateral end of the internal auditory
canal.
 The internal auditory canal is
skeletonized through the entire
length.
 Bone is removed around the porus
acusticus, uncovering the dura of the
posterior fossa.

39. 38

40. 39

41. 40

42. 2. Retrosigmoid approach
The key steps in the operation are:
(1) craniectomy,
(2) exposure of the CPA,
(3) exposure of the IAC,
(4) tumor resection,
(5) hemostasis,
(6) IAC closure,
(7) craniotomy closure
41

43. 42
 exposure of the internal auditory canal during
the retrosigmoid approach.
 After localization of the porus acusticus
through palpation with a ball hook, an H-shaped
dural incision is created over the long axis of
the internal auditory canal.
 Dural flaps are reflected anteriorly and
posteriorly to expose the posterior aspect of
the petrous pyramid.
 Before drilling, Gelfoam pledgets are
positioned above and below the 7 to 8
neurovascular bundle in the posterior fossa to
minimize the spread of bone dust onto
arachnoidal surfaces.

44.  A diamond burr is used to create
deep troughs around the internal
auditory canal, to provide adequate
room for microdissection with the
angled instruments needed to
remove the facial nerve from the
tumor safely.
 Particular care should be exercised
while the superior trough is
developed because the facial nerve
may lie immediately beneath the
dura in this location
43

45.  After the intracanalicular portion of the
tumor is debulked, the lateral most extension
of the tumor is reflected medially, and the
plane between the tumor capsule and facial
nerve is developed.
 This maneuver ensures complete removal of
the tumor from the fundus.
44

46.  The main portion of the tumor in the
cerebellopontine angle is rapidly debulked.
 To facilitate rapid and safe tumor removal, we
use a Cavitron ultrasonic aspirator (CUSA).
 The tumor capsule is first liberated from the
cerebellum and middle cerebellar peduncle.
 The pontine surface, including root entry zones
of CN VII and VIII, can be exposed.
45

47.  Closure of the IAC defect at completion of
retrosigmoid craniotomy.
 After waxing of cut bony walls to seal any
transected air cells, muscle graft harvested
from the nuchal area is mortised into a
bony defect.
 The graft is retained in position by sutures,
which are anchored in dural flaps previously
developed from the posterior petrous
surface
46

48. To summarize
47

49. Complications:
 Intracranial vascular complicatons: posterior fossa hemorrhage,
supratentorial hemorrhage.
 Cerebellar complications: infarcts,
intra-cerebellar bleed,
cerebellar oedema.
 Incomplete tumour removal: more in retrosigmoid approach
 Facial nerve damage: more in middle fossa approach
 Pneumocephalus: Rare complication of retrosigmoid approach
 Injury to cranial nerves: V, VII, IX, X, XI, XII
 Meningitis, encephalitis, cerebritis
48

50.  CSF leak: can be cerebrospinal fluid rhinorrhoea or otorrhoea
 Systemic complications: Pulmonary embolism, SIADH.
 Vertigo and imbalance: Due to prolonged retraction of cerebellum
 Seizures : after middle fossa surgery
 Dysphasia and nominal aphasia
49

51. In the next session, we’ll discuss about
STEROTACTIC RADIOSURGERY…….
51

52. References
1. Scott-Brown’s Otorhinolaryngology Head and Neck Surgery 8th ED
2. Cummings OTOLARYNGOLOGY–HEAD AND NECK SURGERY, 6th ED
3. Brackmann OTOLOGIC SURGERY 4th ED
4. Bachi T Hathiram ATLAS OF OPERATIVE OTORHINOLARYNGOLOGY AND HEAD & NECK SURGERY
52

53. 50
Thanks!