Vestibular schwannoma

Question 1

Where do vestibular schwannomas arise from?

Answer 1

The schwann-cell sheath of the superior division of the vestibular nerve (NOT the acoustic nerve).

Question 2

Are vestibular schwannomas histologically malignant or benign?

Answer 2

Benign.

Question 3

What chromosome is implicated in the growth of vestibular schwannomas?

Answer 3

Loss of a TSG on the long arm of chromosome 22. This is a somatic mutation in sporadic cases, but is inherited or a new mutation (that may be inherited to offspring) in NF2.

Question 4

What percentage of intracranial tumours do vestibular schwannomas make up?

Answer 4

Approximately 8-10% in most series (common tumour).

Question 5

What is the annual incidence of vestibular schwannoma?

Answer 5

1.5 cases per 100,000 population.

Question 6

After what age do vestibular schwannomas usually become symptomatic?

Answer 6

Age 30.

Question 7

What percentage of vestibular schwannomas are unilateral?

Answer 7

At least 95%.

Question 8

Are bilateral vestibular schwannomas pathognomonic of NF2?

Answer 8

Yes (central neurofibromatosis). Patients <40 with unilateral VS should also be evaluated for NF2.

Question 9

How do the vestibular schwannomas of NF2 vs sporadic cases differ cytologically?

Answer 9

They don’t, cytologically they are identical. NF2 tumours however are more prone to forming grape-like clusters that may infiltrate the nerve fibres, whereas sporadic cases are more likely to displace the eighth nerve.

Question 10

What are some common presenting symptoms of vestibular schwannoma?

Answer 10

(In order of decreasing frequency): hearing loss; tinnitus; dysequilibrium; headache; facial numbness; facial weakness; diplopia; nausea and vomiting; otalgia; change of taste. Type of symptoms closely correlate with tumour size.

Question 11

What clinical triad do most vestibular schwannomas present with?

Answer 11

1. Ipsilateral sensorineural hearing loss
2. Tinnitus
3. Balance difficulties.

Question 12

When vestibular schwannomas grow large, what other features may patients present with?

Answer 12

1. Facial numbness, weakness or twitching;
2. Brainstem symptoms;
3. Hydrocephalus.

Question 13

Describe symptoms attributable to eighth nerve complex compression in the IAC.

Answer 13

1. Unilateral sensorineural hearing loss: typically insidious and progressive (c.f. Meniere’s disease, fluctuates), may be sudden in 10%. Frequently high frequency hearing loss.
2. High pitched tinnitus.
3. Balance difficulties, true vertigo only in 20%.

Question 14

How can a vestibular schwannoma cause sudden hearing loss?

Answer 14

Presumably due to acoustic nerve infarction or acute occlusion of the cochlear artery. May be the presenting feature in 1-14%.

Question 15

Name 4 treatment options for sudden hearing loss.

Answer 15

1. Steroids
2. Heparin: has been shown not to help
3. Conservative management: bed rest, salt restriction, no alcohol or tobacco
4. Experimental: thrombolysis with rt-PA

Question 16

Describe symptoms attributable to 5th and 7th nerve compression.

Answer 16

1. Otalgia
2. Facial numbness and weakness (a rare or late occurrence, even though the 7th is almost always distorted early; paradoxically numbness often occurs sooner, despite the 5th being farther away)
3. Taste changes