Acoustic Neuroma

Acoustic neuroma is a non-cancerous tumour of the vestibulocochlear nerve. The vestibulocochlear nerve connects the inner ear to the brain and comprises two sections. One section transmits sound while the other helps to send information regarding balance from the inner ear to the brain.

Acoustic neuromas – also called vestibular schwannomas or neurilemmomas – usually grow slowly. Although they do not damage the brain, they can put pressure on it as they grow. Larger tumours can press nearby cranial nerves that control the muscles of facial expression and sensation. If tumours become large enough to press on the brainstem or cerebellum, they can be life-threatening.

The early symptoms of acoustic neuroma are often subtle. Many people attribute the symptoms to age-related changes. Hence the visit to the doctor is often postponed and diagnosed at advanced stages.

An initial sign is a gradual loss of hearing in one ear accompanied by tinnitus, or ringing/buzzing in the ear. Very rarely, acoustic neuromas cause sudden and unexplained hearing loss.

Other symptoms which may be present include –

• Facial numbness or a constant or intermittent tingling sensation
• Vertigo – usually not spinning but unsteadiness occurs
• Balance disorders
• Facial weakness
• Change in taste
• Trouble in swallowing
• Hoarseness of voice
• Cognitive disturbance

Clinical consultation should be made at the earliest if any of such symptoms are persistent.

• Vestibular evaluation – Videonystagmography is an important diagnostic tool.
• Audiometry – Conducted to evaluate the hearing acuity of both ears.
• Imaging – Magnetic Resonance Imaging (MRI) of the brain with contrast can confirm the presence of an acoustic neuroma.

There are mainly three modalities of treatment for acoustic neuroma:

1. Observation

Acoustic neuromas are not cancerous, and usually slow-growing. Often doctors monitor a tumour with periodic MRI scans and recommend more aggressive treatment if the tumour grows faster or symptoms become more severe.

2. Surgery

Surgery for acoustic neuromas may involve removing all or part of a tumour. There are three principal surgical approaches for extracting an acoustic neuroma:

a. Translabyrinthine Approach

This method involves making an incision behind the ear and removing the bone behind the ear and some of the middle ear. This procedure is recommended for tumours larger than 3 centimetres. The advantage of this approach is that it allows the surgeon to see the facial nerve clearly before removing the tumour. The disadvantage of this technique is that it results in a permanent hearing loss.

b. Retrosigmoid/Suboccipital Approach

This method involves exposing the back of a tumour by opening the skull near the back of the head. This approach can be used for removing tumours of any size and offers the possibility of preserving hearing.

c. Middle Fossa Approach

This approach involves removing a small piece of bone from the ear canal to access and remove small tumours confined to the internal auditory canal, the narrow passageway from the brain to the inner ear. Middle Fossa approach lets the surgeons preserve the patient’s hearing ability.

3. Total Endoscopic Resection

A newer, less invasive technique called total endoscopic resection allows surgeons to remove acoustic neuromas using a small camera interpolated through a hole in the skull. This method is offered only at selected medical centres by highly trained surgeons. Initial studies claim success rates on par with conventional surgery methods.

4. Radiation Therapy

Radiation therapy is recommended in some patients of acoustic neuromas. Ultra-modern techniques used in this treatment makes it possible to send high doses of radiation to a tumour while limiting exposure and damage to the tissue around the tumour.

There are two widely accepted ways in which radiation therapy is used on the patients. Either one of them is used to treat the patient.

5. Stereotactic Radio Surgery (SRS)

Single-fraction stereotactic radiosurgery, in which multiple small beams of radiation are targeted at a tumour in a single session.

6. Fractionated Stereotactic Radiotherapy (FRS)

Multi-session fractionated stereotactic radiotherapy, which delivers lower doses of radiation every day, for several weeks. Studies imply that multi-session therapy may protect the hearing ability of the patients better than SRS.