An acoustic neuroma (also known as a vestibular schwannoma) is a benign tumour that originates from the eighth cranial nerve. This nerve passes from the brainstem to the inner ear and is involved in the transmission of sound and balance from the inner ear to the brain. The eighth nerve is closely associated with the seventh nerve, as they run together in the internal auditory canal to the inner ear. The seventh nerve is responsible for the motor supply of muscles for facial expression. Therefore if the nerve is damaged, the facial muscles weaken. Acoustic neuromas are a slow growing tumour and they generally arise from the vestibular nerves. As they grow in size they can affect the balance and hearing nerves, resulting in symptoms such as deafness, loss of balance and tinnitus. If the tumour gets very large it can cause numbness of the face and facial weakness, or compression of the brainstem, causing stroke-like symptoms of arm and leg weakness.
Tumours are typically described as small (less than 1.5cm), medium (1.5 to 2.5cm) or large (more than 2.5cm).
There are three treatment options available to patients; observation, surgery and radiation therapy or “radiosurgery”.
Choosing the best therapy is a decision made by both the patient and the surgeon after consideration of the patient’s age,
symptoms, health, tumour size and hearing ability. Surgical treatment options for the removal of an acoustic neuroma include the translabyrinthine approach, the retrosigmoid/sub-occipital approach and the middle fossa approach. The choice of approach is based on factors such as tumour size, location, surgeon preference and whether hearing preservation is a goal.
The main objective of the surgery is tumour removal without causing neurological damage or other complications. However, facial nerve preservation is also an important objective. The larger the tumour, the more difficult it is to preserve the nerve.
This nerve is closely applied to the tumour and if damaged, facial weakness results. This can be permanent and causes a significant cosmetic effect with facial drooping. Severe facial weakness can impair eye closure, resulting in corneal dryness, ulceration and even blindness if not managed. It is therefore very important to preserve the facial nerve.
* Illustrations from www.anausa.org