Brain Tumors

An acoustic neuroma , correctly called a vestibular schwannoma, is a benign primary intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve (CN VIII).The correct medical term is vestibular schwannoma, because it involves the vestibular portion of the 8th cranial nerve and it arises from Schwann cells, which are responsible for the myelin sheathin the peripheral nervous system.It comprises 5-10% of all intracranial neoplasmsin adults. Incidence peaks in the fifth and sixth decades and both sexes are affected equally.

Acoustic neuromas may occur sporadically, or in some cases occur as part of von Recklinhausen neurofibromatosis, in which case the neuroma may take on one of two forms.

• In Neurofibromatosis type I, a schwannoma may sporadically involve the 8th nerve, usually in adult life, but may involve any other cranial nerve or the spinal root. Bilateral acoustic neuromas are rare in this type.
• In Neurofibromatosis type II, bilateral acoustic neuromas are the hallmark and typically present before the age of 21. These tumors tend to involve the entire extent of the nerve and show a strong autosomal dominant inheritance. Incidence is about 5 to 10%.

The usual tumor in the adult presents as a solitary tumor, originating in the nerve. It usually arises from the vestibular portion of the 8th nerve, just within the internal auditory canal.

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The earliest symptoms of acoustic neuromas include ipsilateral sensorineural hearing loss/deafness, disturbed sense of balance and altered gait, vertigo with associated nausea and vomiting, and pressure in the ear, all of which can be attributed to the disruption of normal vestibulocochlear nerve function. Additionally more than 80% of patients have reported tinnitus (most often a unilateral high-pitched ringing, sometimes a machinery-like roaring or hissing sound, like a steam kettle).

Larger tumors may lead to increased intracranial pressure, with its associated symptoms such as headache, vomiting, and altered consciousness.

Removal of acoustic neuromas may be performed using several approaches. Each approach has its advantages and disadvantages. Microsurgery for acoustic neuroma is the only technique that removes the tumor. Surgery cannot repair damage that has already occurred to the facial or hearing nerves. Choice of surgical approach is based on the patient's age, medical condition, size of tumor, and preoperative hearing thresholds and speech discrimination, as well as other tests such as electronystagmography, imaging, and auditory brainstem response testing.In general , all acoustic tumors with an intracranial diameter of up to approximately 3.5 cm  qualify for Gamma Knife Radiosurgery . Over the years, larger tumors occasionally have been treated successfully with this technique.Patients with large acoustic neuromas - especially older patients - may still prefer the combination of Gamma Knife Radiosurgery and a shunt operation, a considerably less demanding procedure than microsurgical removal.

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