ACOUSTIC NEUROMA

Acoustic Neuroma, also called Vestibular Schwannoma, is a slow growing non-cancerous tumour of the Vestibulocochlear nerve. This nerve is responsible for conducting impulses regarding hearing and balance from the ear to the brain. Acoustic neuroma patients have a malfunctioning gene, which is responsible for production of a tumour suppressor protein that controls the growth of Schwan cells. The tumours arise from Schwan cells which cover the nerve fibres.

As the tumour is slow growing, the symptoms are also slow in being detected by the patient. Some of the complaints include:

Hearing loss; usually seen in only one ear. This hearing loss is slowly progressive.
A ringing or buzzing sound, called Tinnitus, is heard in only one ear.
Facial numbness, weakness or a feeling of tingling on the face.
Unsteadiness or imbalance. However, patients usually do not exhibit observable signs of vertigo or a sensation of spinning.
Change in taste.
Difficulty in swallowing.
Change in voice.

The last 3 symptoms are found in later stages of the disease or in fast-growing tumours, and as the history is deceptive, often these tumours are identified in advanced stages.

Diagnosis

The following tests are conducted to accurately diagnose Acoustic Neuroma.

Audiometry: To detect sensorineural hearing loss in one ear, which is typical in Acoustic Neuroma patients.
Videonystagmography (VNG): This test reveals early signs of abnormality by way of spontaneous nystagmus, or rapid involuntary movements of the eyes, which may be vertical, direction changing, or hyperventilation-induced.
MRI of the brain: Imaging of the brain by MRI with contrast injection is considered the gold standard to detect even small tumours of 1-2mm size, which may be missed by the less invasive CT scan.
Auditory Brainstem Response (ABR): A sensitive test to record the transmission of sound impulses through different parts of the auditory system. Patients of acoustic neuroma may present ABR findings like interaural wave V latency prolonged.

treatment

As Acoustic Neuromas are benign, slow-growing tumours, their growth is monitored through serial MRIs and administered conservative management when the following conditions are observed:

Less than 0.5cm tumours with no neurological signs;
Elderly patients to avoid morbidity associated with surgery except if cerebellar signs are seen;
Tumour in only hearing ear; and
Poor general condition of patient.

However, more aggressive treatment options are required in tumours causing symptoms of compression, and include surgery and radiation.

Surgery

The decision to operate depends upon the level of hearing loss, the size of the tumour and the general condition of the patient. The main approaches are:

Trans labyrinthine approach: This procedure is preferred for tumours that are larger than 3cm. It involves an incision behind the ear and drilling out the mastoid bone. This approach reduces the risk of facial nerve injury because it allows full exposure of the facial nerve. The disadvantage of this procedure is that it leads to complete and permanent hearing loss.
Retrosigmoid-retro labyrinthine or sub-occipital approach: This procedure can be used for tumours of any size. It also has the advantage of preserving the patient’s hearing. In this technique, the incision is made further back on the skull behind the ear.
Middle fossa approach: This technique is favoured for tumours less than 0.5cm in size.
Endoscopic resection: The surgeon uses endoscope to remove the tumour through a small hole drilled in the skull. This technique is only available in a few centres around the world and the surgeon must be highly skilled and trained.

Radiation

Radiation is used to shrink and kill the tumour cells. It may be recommended looking at the size and shape of the tumour, and the patient’s age and general health. It is also advised if the tumour is difficult to reach surgically to decrease its size. Radiation may be of the following types:

Stereotactic radiosurgery: In which a precisely targeted beam of radiation is used to shrink the tumour without damaging surrounding vital structures. Usually this can be done as a day-care procedure.
Intensity modulated radiation therapy (IMRT): This technique involves delivery of high doses of radiation directly to the tumour after feeding the precise dimensions and location of the tumour into the software of the delivery device. This is considered to be a very safe treatment option.
Image guided radiation therapy (IGRT): This technique uses real-time imaging with CT scans to deliver precise radiation to the tumour without any risk of movement of the patient during the procedure.