Acoustic neuroma

• Disease Site
• Incidence
• Predisposing Factors
• Macroscopic Features
• Microscopic Features
• Natural History
• Clinical History
• Clinical Examination
• General Investigation
• Specific Investigations
• Prognosis
• Treatment Overview
• References

Disease Site

Acoustic neuroma (also known as vestibular schwannoma, neurinoma, neuromas) is a benign tumour of the Schwann cells that surround the vestibulocochlear (XIIth) cranial nerve. The XII nerve sits within the temporal bone in the skull. Acoustic neuroma is responsible for balance and hearing as it relays nerve impulses from the cochlea.

Below is an MRI scan image of a person who has developed an acoustic neuroma:

Incidence

Acoustic neuromas occur throughout the world. No ethnic groups are known to be affected disproportionately. Symptomatic neuromas are estimated to affect between 1 in every 3,500 to 5 in every million people. They are more common in men and between the ages of 30-60 years.

Predisposing Factors

The cause is unknown. A small proportion of people also have neurofibromatosis type 2 (a hereditary condition).

Macroscopic Features

Acoustic neuromas have well defined borders that are attached to the nerve, but can be separated from it. Acoustic neuromas are often firm grey masses.

Microscopic Features

Acoustic neuromas generally stem from the midpoint of the vestibulocochlear nerve. The microscopic appearance can show either tightly packed (Antoni A) or loosely packed (Antoni B) cells.

Natural History

Acoustic neuromas are very slow growing. They generally originate within the internal auditory canal and may cause bony erosion as they expand. A neuroma will first compress the XII^th then VII^th cranial nerves. An untreated tumour will protrude into the cerebellopontine angle and may compress the V^th cranial nerve and eventually the brainstem.

Clinical History

Hearing loss is the most common symptom. The severity and onset varies but is often mild and may easily be overlooked. Tinnitus (ringing in the ear) may also accompany hearing loss. Other symptoms include: vertigo (dizziness), unsteadiness, feeling of fullness in the ear, facial numbness or tingling.

Clinical Examination

A neurological examination, including examination of all cranial nerves can help reveal the presence and/or extent of an acoustic neuroma.

General Investigation

Hearing tests are performed including routine audiological tests and speech discrimination.

Specific Investigations

An auditory brainstem response test can reveal abnormalities associated with the XII^th cranial nerve and suggest further radiological testing. An MRI is the gold standard for diagnosis with gadolinium used as contrast. A CT Scan will pick up most acoustic neuromas, however, small tumours confined to the internal auditory canal may not be evident on a plain CT scan.

Prognosis

Prognosis depends upon the size of the tumour and the extent of its growth. Most are fully resectable; however, some symptoms may remain post operatively.

Treatment Overview

Observation is recommended in patients with asymptomatic neuromas or in patients who are high risk for surgery. Observation includes regular MRIs.

Surgery is the only way to remove the tumour completely. Microsurgery allows preservation of hearing when resecting small tumours.

Patients are monitored in intensive care post operatively to avoid complications.

Stereotactic radiation therapy (radiation surgery) is an option for patients who are high risk for surgery, have small tumours or tumours on both sides.

References

1. Acoustic neuroma [online]. Minneapolis, MN: University of Minnesota; 2002 [cited 11 August 2002]. Available from: URL link