UPDATE IN ACOUSTIC NEUROMAS

by: Gil Lederman, M.D.

Acoustic neuroma treatment is undergoing a marked revolution. Acoustic neuromas are benign tumors that affect the eighth cranial nerve - a nerve that comes from the brain and is delicately located adjacent to important other structures such as the facial nerve and brain stem. It is a tumor that affects 2,000 to 3,000 Americans annually.

Those with acoustic neuromas most frequently have diminished hearing. It is often first noticed because of the decreased ability to use a telephone on the involved side. Ringing in the ear, imbalance and later, pain, numbness or weakness of the face can occur.

In the past, treatment remained in the domain of surgeons. Unfortunately, surgery is associated with marked morbidity and occasional mortality. A recent paper from the University of Pittsburgh revealed a complication rate such that more than one-half the patients lost facial function after surgery and a significant number of patients required re-operation for complications from the open surgery. The surgical data was compared to single fraction radiosurgery and a marked diminishment in complications was found using radiation.

Now, enhancement of radiosurgery technique has been developed at Staten Island University Hospital. This data was presented at The 77th Annual American Radium Society meeting in Paris. The data shows excellent control of acoustic neuromas with no complications.

Since multiple modalities of treatment offer good tumor control, the main question is what - if any - side effects are related to treatment. By offering fractionated or divided dose stereotactic radiation, it appears that the side effects can be markedly reduced if not abolished.

The rationale of stereotactic radiosurgery is to render effective care while avoiding damage to normal tissue.

In the data from Staten Island University Hospital, twenty-six patients with 27 acoustic neuromas were treated with fractionated stereotactic radiation. One patient had bilateral acoustic neuromas and received this treatment to both tumors. Fourteen patients had left-sided acoustic neuromas, eight had right-sided tumors and four had a history of bilateral tumors. Four patients (14.8%) had prior surgery.

Prior to any procedure, Informed Consent was signed with all questions answered and all risks, benefits and alternatives explained. The options always included, at least, observation of the tumor, invasive surgery and other methods of radiation.

The data included patients ranging from 35 to 89 years of age. Treatment was carried out using a Varian 2100-C linear accelerator and a relocatable head frame. This head frame is non-invasive and avoids the pins in the head that other methods of radiosurgery require. Most patients received four or five treatments depending on the size and configuration of the tumor. Follow up included physical examinations, MRIs and audiograms.

A tumor is considered controlled after radiosurgery if the tumor stops growing or shrinks in size. In fact, the data showed a 100% control rate with the majority of tumors decreasing in size. Of 18 tumors greater than 4 cubic centimeters in size, the majority (66.7%) shrunk. The remainder showed cessation of growth. None increased in size.

For patients undergoing audiometry or hearing evaluation, 37.5% had improvement and 25% had stabilization. Twenty-five percent had hearing that had worsened and 12.5% of patients had no hearing prior to treatment. Of patients with imbalance, 89.5% had improved balance after this pinpoint precision radiation. There has been no hair loss associated with fractionated stereotactic radiation.

No patient had facial nerve weakness or paralysis after treatment. This is in marked contrast to those patients undergoing single fraction radiosurgery or open surgery. Single shot radiosurgery has been associated with a 20% risk of facial nerve damage compared to open surgery's 50% damage rate. The surgical data quoted above consists of only patients with smaller acoustic neuromas measuring 3 centimeters or less in diameter.

Pollock et al in The Journal of Neurosurgery evaluated facial nerve dysfunction as a result of open surgery as compared to single shot radiosurgery. They wrote, "Microsurgery was associated with a greater incidence of peri-operative or delayed facial dysfunction (52% versus 23%, P<0.01) and long-term post operative facial paresis (37% versus 17%, P<0.05)."

Of interest is the fact that Staten Island University Hospital's group is comprised of patients with both small and large sized tumors. In dramatic contrast to surgery and single shot radiation, no patient reported any complication or needed any subsequent medical or surgical intervention.

No facial weakness was seen in our group treated with fractionated stereotactic radiation. Thus, the fractionated radiosurgery stands out from the facial function point of view while maintaining the high control rate.

Concluding remarks in Paris noted that fractionated stereotactic radiation based upon treatment at Staten Island University Hospital showed a high control rate (100%), a chance at maintaining or possibly improving hearing and imbalance while avoiding treatment-related complications, hospitalizations or the need for post treatment surgery. No patient in this group required surgical intervention after stereotactic radiation. This data reflects a long stride in the achievement of successful therapy for acoustic neuromas in patients formerly caught between an ill-placed tumor and treatment associated with severe complications. Continued follow-up will confirm the efficacy of treatment.

As the Chinese proverb says, "A long journey starts with a single step."

reprinted: 2/98