Acoustic Neuroma (Vestibular Schwannoma)

A benign (non-malignant) tumor that arises from Schwan cells that surround the Vestibular Nerve (part of the Eighth Cranial Nerve complex). Schwann cells serve a particular function to form myelin, the insulating portion of nerves that are outside the brain and spinal cord.

As with most intracranial tumors, the exact cause of these tumors is unknown.

SYMPTOMS

Tumor size is closely correlated to the types of symptoms experienced by these patients. One-sided hearing loss, ringing in the ears, and problems with equilibrium (dysequilibrium) are related to pressure on the 8th cranial nerve. The hearing loss is slowly progressive in most patients and is often first noticed as difficulty in hearing conversation while on the telephone. The ringing in the ears is high pitched.

As the tumor grows larger and causes pressure on the 5th (trigeminal) and 7th (facial) cranial nerves, facial numbness, facial weakness and changes in taste occur. Larger tumors can also cause pressure on the brain stem potentially resulting in the following symptoms: difficulty with balance, headache, nausea/vomiting and double vision. A large tumor can also create pressure on the lower cranial nerves causing difficulty swallowing and hoarseness.

Symptoms occur with varying frequency:

• Hearing loss – 98%
• Ringing in the ears – 70%
• Dysequilibrium – 67%
• Headache – 32%
• Facial numbness – 29%
• Facial weakness – 10%
• Double vision – 10%
• Nausea/vomiting – 9%
• Change of taste – 6%

DIAGNOSIS

Thin Slice Contrast MRI is the most accurate and useful diagnostic test for this tumor. The MRI reliably identifies 98% of tumors and has almost no false positive risk. The characteristic finding is a round or oval-shaped tumor centered on the Internal Auditory Canal. Large tumors may show cystic appearing areas. CT scan with contrast is the second procedure of choice. The CT scan gives good information about the bony landmarks surrounding the tumor; its soft tissue imaging, however, is less well defined compared with MRI scans.

Audiometric and Audiologic Studies are done as baseline studies to determine the function of hearing on both sides with particular attention to the affected ear. Pure tone audiograms are useful as an initial screening test since they identify high tone hearing loss.

TREATMENT OPTIONS

Surgery

This is generally the best treatment option for most patients. There are different surgical approaches determined by the size and location of the tumor, the symptoms of the patient and the surgeon’s operating preference. It is possible to save the patient’s hearing in a selected minority of cases.

The goal of surgical management in most cases of Acoustic Neuromas is total removal of the tumor without complications. There are clinical instances, however, where the surgeon leaves tumor behind rather than risk the chance of serious neurological injury. The options for management of patients with residual tumor include Stereotactic Radiosurgery, repeat operation at a later date, or following the tumor size with MRI scans.

Stereotactic Radiosurgery

For many patients with small or medium sized tumors, Cyberknife and other types of stereotactic radiosurgery is rapidly becoming the preferential treatment of acoustic neuromas. Radiosurgery is more effective for smaller tumors. The goal of radiosurgery is to hopefully prevent the tumor from getting any larger.

The advantages of radiosurgery are that it is non-invasive, easily tolerated and effective in controlling tumors of limited size. Consequently, stereotactic radiosurgery becomes a viable treatment option for patients with residual tumor after surgery, elderly patients and/or patients who have multiple medical problems making open surgery too risky.

Observation

Some acoustic neuromas grow slowly or not at all; 6% actually decrease in size. This option is typically open to patients who have a very small tumor and are without many symptoms, or elderly patients with many medical complications with a small to medium sized tumor. These patients need to understand that in time the tumor will probably cause complete hearing loss in the affected ear.

Periodic MRI scans are performed to follow the size of the tumor.