Acoustic Neuroma
D E FI N I T ION
Schwann cell-derived tumours that commonly arise from the vestibular
portion of the eight cranial nerve. More than 90% of cases are unilateral. Bilateral cases
are seen in neurofibromatosis type 2.
AETIOLOGY
Risk factors include:
. Neurofibromatosis type 2.
. Exposure to loud noise.
. Childhood exposure to low-dose radiation for benign conditions of the head and neck.
EPIDEMIOLOGY
Incidence is one in 100 000 per year. The median age at diagnosis is
approximately 50 years. Account for8%of all intracranial tumours in adults and 80–90%
of cerebellopontine angle tumours.
HISTORY
Symptoms of cranial nerve compression by the tumour:
VIII nerve: Hearing loss (95%), tinnitus and unsteadiness while walking.
V nerve: Facial numbness, paraesthesia and pain (17%).
VII nerve: Facial weakness (6%).
With tumour progression (expansion into the cerebellopontine angle):
Compression of the cerebellum resulting in ataxia.
Compression of the lower cranial nerves (IX, X and XI) resulting in dysarthria and dysphagia.
EXAMINATION
Abnormal cranial nerve examination:
VIII nerve: Hearing loss, the Weber and Rinne tests suggest asymmetric sensorineural hearing
impairment, nystagmus (beating away from tumour).
V nerve: Loss of corneal reflex, facial numbness.
VII nerve: Lower motor neuron facial palsy.
Cerebellar compression: Ipsilateral ataxia and nystagmus.
Look for signs of neurofibromatosis.
INVESTIGATIONS
Audiometry: Asymmetric sensorineural hearing loss.
Brainstem-evoked response audiometry: Delay in nerve conduction time on the affected side.
MRI with gadolinium contrast: Sshows acoustic neuromas in the region of the internal
auditory canal with variable extension into the cerebellopontine angle.
MANAGEMENT
Surgery is aimed to prevent further disability and does not restore hearing.
There are three operative approaches: retromastoid suboccipital, translabyrinthine and
middle fossa.
Radiation therapy: Stereotactic radiosurgery (using multiple convergent beams to deliver a
high single dose of radiation) may be considered for neuromas<3 cm and in patients unfit
for surgery. Stereotactic radiotherapy (using focused doses of radiation given over a series
of treatment sessions) and proton beam therapy may also be used. The choice of therapy
depends upon the availability of the appropriate expertise and patient preferences.
COMPLICATIONS
Compression of brainstem and the fourth ventricle resulting in hydrocephalus,
increased intracranial pressure and death can occur in untreated cases.
PROGNOSIS
Hearing loss is often permanent. Treatment merely prevents further damage
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