ACOUSTIC NEUROMA

Acoustic neuromas are being more frequently diagnosed as those with hearing loss and sometimes other symptoms are obtaining MRIs (Magnetic Resonance Imaging scans) which can show small tumors at an early stage.

The several names used for this benign tumor include acoustic neuroma, acoustic neuronoma and vestibular schwannoma. It involves the 8th cranial nerve which has two branches - acoustic and vestibular and under the microscope resembles schwann cells. For that reason, vestibular schwannoma is a synonym.

The phrase "benign" generally implies a course unmarked by progression or death. Unfortunately, in the brain, this is not necessarily the situation. Because the brain is so delicate and encased in bone, there is little extra space for unusual growths of any type.

The incidence of acoustic neuromas is modest - approximately 1 per 100,000 people per year. It's equivalent to approximately 2,500 people being diagnosed each year in the United States. That is of little relief to those diagnosed. Because MRI can detect lesions which were previously not visible by other means, it is likely that the true incidence is higher.

Symptoms include decreased hearing, ringing in the ears and a change in balance. While acoustic neuromas can affect either ear and sometimes both ears, most often it is unilateral.

The vast majority have asymmetric loss in hearing. Most commonly it is a high frequency hearing loss but some will have normal hearing - or symmetric hearing with modest diminishment or distortion. An early sign is avoiding one ear while using a telephone.

As the tumor grows, it can encroach on the adjacent brainstem. This may create headaches, difficulty walking and damage to cranial nerves. Cranial nerves are neurologic structures that originate from the brain performing certain motor or sensory functions.

Late symptoms are pain, numbness or weakness in the face. With increasing size, progressive symptoms include nausea, vomiting and even coma, respiratory depression and death.

People with bilateral acoustic neuromas commonly have an inherited disease called neurofibromatosis. By radiographic appearance there is no difference between the sporadically occurring unilateral acoustic neuromas and the bilaterally occurring disease. The bilateral type is usually more aggressive in its invasion, however.

Much acoustic neuroma data was presented at a National Institute of Health Consensus Development Conference. In a subsequent report, it was noted that "tumors tend to enlarge unpredictably. Some do not change size for many years, while other may grow at the rate of up to 20 millimeters in diameter per year."

The Consensus report stated "all cases of vestibular schwannomas are thought to result from the functional loss of a tumor suppressor gene which has been localized to the long arm of chromosome 22. In at least 95% of patients, however, the disease is unilateral and the majority of these cases are sporadic, resulting from somatic mutation that are not associated with an increased risk for other tumors in either the individual or close relatives."

The Consensus report addressed the who and when of treatment. It was felt that since most at diagnosis have a symptomatic tumor, treatment should be carried out quickly. Especially included in this group were the young with progressive neurologic deficits or evidence of tumor growth.

With MRI detecting small lesions, the natural history is unknown. An option is follow-up scans to determine the growth rate. The consensus panel alludes to "the risk of neurologic deterioration in conservatively managed patients."

Traditionally, radiation has been used in those who refuse to undergo invasive surgery. The National Institute of Health's panel writes that, "the greatest experience to date has been with stereotactic radiosurgery." They wrote that "early reports indicate the retardation of tumor growth as observed in the majority of patients."

Peri-operative surgical complications can include air embolism, intracranial hemorrhage and stroke. "Cerebral spinal fluid leak and meningitis can occur in a delayed fashion and also can require immediate therapy."

"Loss of hearing in the operated ear is the most common adverse consequence and can be a serious handicap. These patients have difficulty in even modestly noisy environments and do not have directional hearing", the NIH panel reported.

Also reported by the panel was the fact that "abnormal vestibular function occurs in almost all patients." Additionally noted was "one distressing complication of surgery is disfiguring facial nerve weakness or paralysis with consequent physical, emotional, psychosocial and possibly professional dysfunction." The panel reported treatment approaches to "reanimation" of the face includes surgery and physical occupational therapy. "As yet, none of these can restore normal function appearance." Also discussed were other cranial nerves being damaged by surgery including the fifth, seventh, ninth, tenth and twelfth. The panel describes recurrence after surgery where the tumor was apparently either totally or partially removed; thus all cases need to be followed by imaging. Those that have recurred may be managed by re-operation, fractionated stereotactic or standard radiation.

Stereotactic radiosurgery avoids all cutting, bleeding and anesthesia. The panel reported that "stereotactic radiosurgery, a newer modality has benefit of a low early complication rate, but unknown long term complications." New approaches developed since the National Institute of Health Consensus meeting are lower radiation dose for stereotactic radiosurgery as well as fractionated radiosurgery.

Traditionally, fractionated radiation divides the total dose into smaller segments in an attempt to protect vital surrounding tissues. Normal tissues may repair radiation changes while tumors accumulate the radiation damage.

Our recently submitted data that has been accepted by the European Neuro-Oncology meeting in Holland shows a very high control rate. All patients having received radiation have had cessation of growth or shrinkage of the tumor. Furthermore, a significant share of patients with symptoms have had an improvement. There have been no patients who have suffered facial nerve damage unlike single fraction radiosurgery.

Fractionated stereotactic radiation is an alternative to invasive surgery. After radiosurgery, people return to their normal activities essentially immediately with no recuperatory period. The vast majority undergoing stereotactic radiosurgery for acoustic neuromas have cessation of growth or more commonly, dramatic shrinkage in the size of the tumor.

The goals of stereotactic radiosurgery in the treatment of acoustic neuromas as well as metastases, meningiomas, arteriovenous malformations and brain tumors are obviously to stop tumor growth, avoid invasive surgery and eliminate the need for any surgical intervention as best as possible.

Stereotactic radiosurgery is a viable option for those who seek successful treatment without invasive surgery.