A BRIEF QUOTE ABOUT ACOUSTIC NEUROMA

1. ACOUSTIC NEUROMA
Dr.AJAY MANICKAM

2. Misnomer
 Neither “acoustic” , nor neuroma.
 Schwann cells of vestibular division of eighth
cranial nerve
 In 1992, NIH Consensus Development
conference adopted the standard
terminology….

3. VESTIBULAR SCHWANNOMA

4. Skull base
 Composed of ethmoid,
sphenoid, occipital,
frontal & temporal
bones

5. Cerebellopontine angle
 Fluid-filled space of lateral
cistern
 Anterior – postr surface of
petrous bone
 Posterior – antr surface of
cerebellum
 Medial – inferior olive
 Superior – infr border of pons &
cerebellum
 Inferior – cerebellar tonsil

6. Arteries in CPA
 Loop of AICA often
traverses between the
7th & 8th cranial nerves
at their brainstem
entry site.

7. Tumours of CPA
 Vestibular schwannoma –
91.3%
 Meningioma – 3.1%
 Epidermoids – 2.4%
 Non-vestibular
schwannomas – 1.4%
 Arachnoid cysts – 0.5%

8. V.S. - epidemiology
 Most common skull-base neoplasm
 Most common temporal bone neoplasm
 6% of all intracranial tumours
 91% of CPA tumours
 No racial or gender predilection

9. Forms of V.S.
Sporadic With Neurofibromatosis
 95% of allVS
 Unilateral
 5th-6th decade of life
 NF type 2
 5% of allVS
 Bilateral
 Younger age
 NF type 1
 2% of NF1 develop unilateralVS

10. Pathogenesis
Obersteiner-Redlich zone  Originates within IAC
 Superior : inferior = 1:1
 Vestibular nerve myelination :
proximally by oligodendroglial
cells & distally by schwann cells
 Junction is the O-R zone,
situated near vestibular /
Scarpa’s ganglion, rich in
scwann cells

11. Genetics
 Chromosome 22q12 defect
 Sporadic – “double-hit” of 2
normal genes
 NF2 – 1 defective gene;
“single-hit” is enough
 Gene product – MERLIN –
inhibits IP3

12. Pathology - gross
 Smooth surface
 Bright yellow to gray in
colour
 Large tumours are often
cystic
 Unencapsulated
 Soft & friable to firm &
rubbery

13. Pathology - microscopic
Antoni A Antoni B
Densely packed-cells with small
spindle shaped nuclei
Loosely-arranged, vacuolated,
pleomorphic cells

14. Verocay body
Whorled pr palisading variety of Antoni A cells
Stains +ve for S-100 immunoperoxidase, neuron-specific enolase & vimentin

15. Growth pattern
 Benign, slow-growing tumour – 0.2cm / year
 Grows by cellular proliferation
 Tumor involution –
1. Spontaneous decompression of cystic areas
2. Tumour outgrowing blood-supply
 Rapid tumour expansion –
1. Cystic degeneration
2. Intratumour bleeding

16. Stages of growth
Intracanalicular – within IAC
Cisternal – displaces CSF,
AICA, 7th & 8th nerve

17. Brainstem compression –
touches laterlal pontine
surface & displaces 5th nerve
Hydrocephalic stage – 4th
ventricle effaced secondary
to brainstem compression

18. Clinical presentation
 Hearing loss –
 MC presenting feature
 Unilateral
 Sensorineural, initially at higher frequencies
 Sudden-onset SNHL in 26% cases
 Poor SDS score, disproportionate to PTA values

19. Cont.
 Tinnitus –
 2nd most common symptom >50% cases
 Constant
 Unilateral
 High-pitched

20. Cont.
Vertigo –
 Slow reduction of vestibular function –
central compensation – vertigo is rare
 Occurs in smaller tumours where
considerable vestibular function remains
 Self-resolving ( days to weeks )

21. Cont.
Dizziness –
 In brainstem compression stage of larger mass
 Due to uncompensated peripheral vestibular
disturbance & cerebellar compression
Large tumours compressing cerebellum –
 Dysmetria
 Truncal ataxia
 Hemiplegia, increased DTR ( long tract problem)

22. Cont.
 Trigeminal nerve dysfunction –
 Absent corneal reflex – earliest manifestation
 Mid-face hypoesthesia
 Occurs in brain-stem compression stage
 Occasional facial pain
 Motor fibres are more resistant to stretch than
sensory – so unilateral temporal wasting, masseter
atrophy & secondary malocclusion is rare.

23. Cont.
Facial nerve dysfunction –
 Rare as it is very resistant to stretch
 Hypofunction ( weakness / palsy ) or
hyperfunction (spasm or twich of orbicularis
oculi )
 Histelberger’s sign – hypoesthesia of postero-
superior part of EAC & conchal bowl
 Always exclude facial schwannoma

24. Cont.
Eye manifestation -
 Horizontal nystagmus beating away from
tumour side due to vestibular hypofunction
 Vertical nystagmus in brainstem compression
 Hydrocephalic stage – papilloedema, optic
atrophy, blindness – rare.

25. Investigations
Audiogram
 Unilateral, down-
sloping, high-frequency
SNHL
 Disproportionate SDS
score
 Screening tool

26. MRI
Gadolinium enhancement
 Central
hypointense
areas
represent
cystic
change

27. MRI – cont.
Ice-cream cone appearance NF2

28. BERA
 Most sensitive & specific audiological test
 Replaced by MRI as principal investigation
 BERA normal – 10-15% cases
 No waves – 20-30% cases
 Only wave 1 – 10-20% cases
 All waves present with delayed wave 5 latency – 40-60%
 Good hearing prognosis – no wave 5 latency with
preservation of wave 3

29. ENG
 Reduced ipsilateral response with horizontal
nystagmus is seen
 Poor specificity – not usually done
 Has prognostic value – if ‘–ve’ caloric test –
1. Less post-op vertigo
2. Better hearing outcome ( caloric –ve in LSC
involvement i.e. superior vestibular nv, which is
away from cochlear nv )

30. Treatment options
Observation
with serial
imaging
Microsurgery
• Translabyrinthine
• Retrosigmoid
• Middle cranial
fossa
Stereotactic
radiation

31. Goals of management
1
• Preservation of life
2
• Preservation of facial function
3
• Preservation of hearing

32. Observation
 Where patient can outlive the tumour
 Unfavorable patient factors (aged, poor health)
 Favorable tumour factors ( small, slow-growing )
 Poor surgical candidates
 Serial MRI ( 6monthly in 1st year – then yearly)
 Measure largest extrameatal diameter in axial cut
 Observe if <0.2 cm / year
 If >0.2 cm / year – surgery or radiotherapy

33. Microsurgery options
PTA with SDS
Good hearing
<1 cm – MF
1-2.5 cm – RS
>2.5cm –TL
(or RS if
limited IAC
extension)
Poor hearing TL

34. Complications
 Facial nerve transection – highest in MF
 Hearing loss – highest inTL
 Persistent post-op headache – highest in RS
 Retraction injury – cerebellum in RS, temporal
lobe in MF – encephalomalacia
 CSF leak – more in RS
 Recurrence – least inTL

35. Stereotactic radiotherapy
 Controversial role
 Primary t/t – smaller tumour in old age
 Avoid in young – long-term complications of RT
 Avoid in >3cm tumour – risk of oedema &
secondary brainstem compression
 Indefinite monitoring with MRI
 Good option in recurrence following microsurgery

36. NF2
 Primary management
followed by Auditory
Brainstem
Implantation
preferably in the same
sitting

37. THANK
YOU