Stereotactic radiosurgery may now be the most commonly chosen treatment by patients with acoustic neuromas, also known as vestibular schwannomas. We estimate that there are approximately 2,000 new patients who receive treatment each year in the United States. In 2002, 931 patients had Gamma Knife® radiosurgery. This represented a 430% increase since 1993. Since the rest chose either fractionated radiotherapy, surgical resection or linear accelerator or charged particle radiosurgery, the most common treatment may be Gamma Knife radiosurgery.
What is responsible for the broad acceptance of this approach by both patients and physicians? In this report I will discuss the reasons why many patients choose radiosurgery. For others, the choice of observation, surgical resection, or fractionated radiotherapy may appear to be in their best interests.
Despite much opinion, particularly voiced on the Internet but also from support groups, physicians, and patient discussion, data exist in quality medical journals that can help patients decide between the various options. Some patients become confused by what they perceive as conflicting opinions amongst physicians. Many physicians provide only one kind of treatment and may appear to be biased toward their own approach. What we know from these reports is summarized in this article.
Surgical removal (resection) of the tumor is indicated for patients with larger tumors (>3 cm) which have caused major neurological deficits from brain compression. Surgeons perform stereotactic radiosurgery for small or medium-sized tumors (<3 cm) with the goals of preserving neurological function and prevention of tumor growth. The long-term outcomes of radiosurgery, particularly with the Gamma Knife, have proven its role in the primary or adjuvant management of this type of tumor. It is clear that results after radiosurgery are much more consistent than results following resection, which is highly dependent on an individual surgeon's skill and experience, among other factors. A 2003 report by Barker et al. in the journal Laryngoscope showed that better clinical outcomes were achieved by surgeons and hospitals that treat greater numbers of acoustic patients. Fractionated radiotherapy has been suggested as an alternative for selected patients with larger tumors for whom microsurgery or radiosurgery may not be feasible, or for some patients in an "attempt" to preserve cranial nerve function.
Why is radiosurgery a frequent choice for patients? The opportunity to avoid surgical complications is a major reason, including the risks of spinal fluid leakage, infections, cardiopulmonary complications, hydrocephalus ("water on the brain") and various cranial nerve deficits (facial weakness being the most important). Many patients feel radiosurgery is the best choice for maintaining nerve function and quality of life.
The Long-Term Tumor Response
Experience with radiosurgery now extends to over thirty years. During the late 1980s and early 1990s, patients and their doctors chose radiosurgery or resection based mainly on early outcomes data from limited patient series. In 1987 we began a prospective assessment of the response of patients with acoustic tumors to Gamma Knife radiosurgery.
At our last review, 827 patients underwent stereotactic radiosurgery for an acoustic tumor (vestibular schwannoma) at the University of Pittsburgh over a 15-year interval. These included 765 patients with solitary tumors and 62 with neurofibromatosis type II, a hereditary disease characterized by bilateral acoustic neuromas. Fifty percent of tumors were on the left side of the brain and fifty percent were on the right side, and half of the patients were female. The patient age range was 12 to 95 years (mean, 56 years). Twenty percent had undergone prior surgery. "Useful" hearing before radiosurgery was noted by 33% of patients.
One hundred ninety-two patients had radiosurgery between 1992 and 1997 and were eligible for extended follow-up. The maximum follow-up in this cohort was 65 months. The median tumor margin dose was 13 Gy. Five-year actuarial rates of developing problems were: facial weakness, 1%; facial numbness, 2.6%; hearing level preservation, 71%; preservation of testable speech discrimination, 91%. At a tumor margin dose of =13 Gy, the rate of facial neuropathy was 0%, and above 13 Gy, 2.5% (usually mild and transient). Neuropathy refers to malfunctioning nerves, and symptoms can include weakness, numbness and pain. Tumor diameter did not significantly affect results.
We continue to evaluate a cohort of patients who were treated before 1992 who are a minimum of ten years out from their procedure (n=162). This study represented results of our initial techniques. Approximately 70% of irradiated acoustic tumors decreased in size over time. Nine patients had tumors that increased in size and all were identified within the first three years after radiosurgery. Enlargement represented either true neoplastic tumor growth (n=4) or tumor death (n=5) with an expansion of the tumor margins as the central portion of the tumor became necrotic. In the latter group, patients' subsequent imaging studies confirmed tumor volume regression. Four patients underwent resection. No further increase in tumor volume was identified in any patient with further follow-up. Patients returned to their routine activities immediately. In our five to ten year review, three patients developed hydrocephalus and required a ventriculoperitoneal shunt. All new or worsened post-radiosurgery deficits occurred within 28 months of radiosurgery and no patient described a treatment-related problem after the third year. We continue to tell patients that 2% of them may require tumor resection in the future, a number that is consistent with other groups.
Qualify of Life
There have been a number of patient-based surveys to study outcomes after acoustic neuroma management. One of the first was a survey of 541 patient members of the Acoustic Neuroma Association who provided data on tumor resection between 1973 and 1983. Sixty-two percent reported facial weakness, 84% reported eye-related problems, and depression, sleep disturbance and speech or swallowing difficulties were reported by 38%, 26% and 16%, respectively. More recently, a larger survey of 1579 resections performed between 1989 and 1994 found improved results that included a 44% rate of facial weakness, an 11% rate of cerebrospinal fluid leakage, and persistent balance problems after one year in 9%. Approximately 8% had recurrent or residual tumor on follow-up imaging.
Better results following resection have been documented since that time. Samii et al. and Gormley et al. found that complete tumor removal was a frequent outcome. However, neurologic and systemic morbidity (complications) remained present with 1% mortality rates and cerebrospinal fluid fistula rates of 9.2% (Samii) and 15% (Gormley). The study by Barker et al. evaluated patient death following resection and found a rate of 1 in 200, even amongst surgeons with the most experience. However, for patients with large acoustic tumors (over 3 cm in extracanalicular diameter) and those with progressive neurologic deficits that require brainstem decompression, total or subtotal surgical resection is the preferred option. We believe that a complete resection should be performed in such patients if possible, but not at the expense of lost neurologic function. Stereotactic radiosurgery can be considered for patients with intracanalicular, small or medium-sized acoustic tumors since most such patients do not have a rapidly progressive neurologic syndrome. The initial symptoms caused by most acoustic tumors are not improved by resection.
A recent United Kingdom report by Martin et al. (Table 1) evaluated quality of life in patients after tumor resection. They found a disparity between the patient's report and the physician's assessment of function, with decreases in physical functioning, general health, and social functioning after surgery. More severe balance functions led to worse social functioning.
The long-term effects of both resection and radiosurgery must be documented to assist physician and patient decision making. Surprisingly little information has been published on long-term imaging-based outcomes after resection. Cerullo et al. noted a 10% recurrence rate after 10 years had passed following resection. In their series of over 100 patients in which hearing preservation was attempted during resection, Mazzoni et al. reported that the overall tumor recurrence rate was 8.1%. These papers are often criticized for their results, but they represent an honest evaluation of longer-term imaging results. All groups should strive to obtain serial imaging studies on their own patients. Post et al. found that 4 of 56 patients (7%) had an incomplete resection when hearing preservation was attempted and that three had regrowth of the tumor within three years. In the largest series, Samii et al. reported a complete resection in 98% of patients and found later recurrence in 6 of 880 who did not have neurofibromatosis type II. In our radiosurgery series, 98% of patients required no further surgery and 94% had imaging confirmation of persistent tumor control. Tumors that increased in size in the first year or two after radiosurgery did so usually in association with central tumor necrosis, with a small expansion of the tumor capsule. Most such tumors then regressed below baseline in size with longer follow-up. Such transient expansion may be associated with temporary ear region discomfort, perhaps from regional dural inflammation.
What Is Really Know About Fractionated Radiotherapy?
In the last several years, a number of groups have used fractionated radiation therapy to treat patients with acoustic neuromas. This technique developed when several centers who used linear accelerator irradiation technology were not satisfied with the results or accuracy of their devices after single fraction irradiation (radiosurgery). In order to decrease the cranial nerve morbidities they were observing, they began to deliver radiation over multiple sessions (fractionation). The goal of this approach is to weaken the effect of each radiation administration and try to maintain brain or nerve function. Correspondingly this also weakens the effect of the radiation on the tumor target.
Williams et al. reported 80 patients who had fractionated stereotactic radiotherapy. Median follow-up after radiotherapy was 2.9 years. Seventy patients received 25 Gy in five fractions and ten patients received 30 Gy in ten fractions. The treatment was delivered using CT targeting which is limited in evaluating the intracanalicular portion of the tumor. Only 19 of 80 patients had Gardner-Robertson grade 1 or 2 hearing ("serviceable" to "excellent" hearing) at the time of treatment. Hearing levels were preserved in 82% (actuarial data). Two patients had transient trigeminal neuropathies and no patient had a significant facial neuropathy. There is little data on this approach in the peer-reviewed literature that includes diligent outcomes and follow-up. Standardization with linear accelerator machines, which are made by many manufacturers, does not exist. Therefore, research results with this technology are not as comparable among researchers as with Gamma Knife which is identical throughout the world.
Optimally, appropriate doses of radiation should be delivered precisely to the tumor and regional brain structures should be spared radiation. This is not the case with fractionated techniques where larger volumes of regional tissue are irradiated. We believe that any advantage of fractionation in limiting toxicity only makes sense if the target volume contains normal brain or nerves. Sophisticated stereotactic radiosurgical instruments allow regional brain or nerves to be spared through frame-based, single-session image guidance. We do not believe that fractionated radiotherapy provides any useful advantage over radiosurgical techniques that have been in use for the last 10 years.
What Would Neurosurgeons Choose for Themselves?
A survey was mailed to members of the Congress of Neurological Surgeons in July 2002. Six hundred sixty-three surgeons responded to the survey. The survey included two questions about acoustic neuroma. Forty-one percent of responders were between the ages of 40 and 50. Eighty percent of neurosurgeons surveyed had either performed radiosurgery on a patient with an acoustic neuroma or had referred a patient for neurosurgery (n=530).
Question: You are a 37 year-old neurosurgeon who presents with mild decreased hearing on one side. You have no tinnitus, no balance problems and facial function is normal. An MRI scan shows an intracanalicular acoustic neuroma and serial scans have shown a small amount of growth. Which management strategy would you choose for yourself? (Observation, stereotactic radiosurgery, surgical resection or fractionated radiotherapy.)
Response: The majority of surgeons (43%; n=283) stated that they would choose stereotactic radiosurgery for management of their small acoustic tumor. Only 122 surgeons (18%) stated that they would choose surgical resection of their tumor. Fractionated radiotherapy was chosen by 2% of responders. Interestingly, 240 surgeons (36%) stated that they would continue to observe their tumor rather than undergoing any specific treatment at the present time. It had been stated in the case presentation that serial scans had already shown a small amount of growth. This tumor had been observed and was increasing in volume. Nevertheless, approximately one-third of responders continued to choose observation for a 37 year-old patient with a small but growing tumor. This case reflected the care of an actual neurosurgeon who had Gamma Knife radiosurgery. He remains well 18 months after his procedure and maintains a full practice. He has had no facial weakness or change in hearing.
Table 1. Comparison of Patient Survey Data for Vestibular Schwannomas
Year of Study
No Change in Employment
Offers Positive Recommendations about Treatment
Mean Tumor Size
New Balance Problems
New Onset Tinnitus
New Facial Nerve Dysfunction
1 Martin HC, Sethi J, Lang D, et al. Patient-assessed outcomes after excision of acoustic neuroma: postoperative symptoms and quality of life. J Neurosurg 2001;94(2):211-216.
2 Kondziolka D, Lunsford LD, McLaughlin MR, Flickinger JC. Long-term outcomes after radiosurgery for acoustic neuromas. New Engl J Med 1998;339:1426-1433.
Question: You are a 50 year-old neurosurgeon who presents with mild decreased hearing on one side. You have tinnitus but no balance problems and facial function is normal. An MRI shows a 2.2 cm left acoustic neuroma. Which management strategy would you choose for yourself? (Observation, stereotactic radiosurgery, surgical resection or fractionated radiotherapy.)
Response: In this scenario, the neurosurgeon had a medium size acoustic tumor that indented the side of the brainstem but did not compress the fourth ventricle. The minority of surgeons recommended continued observation for a tumor of this size (6%). Surgical resection was recommended by 347 surgeons (52%), whereas radiosurgery was chosen by 261 surgeons (39%). Fractionated radiotherapy was only chosen by 3%. When the results were stratified by age, resection was the most popular choice across the groups between the ages of 30 and 60. However, radiosurgery became more popular with advancing age of the survey group, surpassing resection as the most popular choice when the neurosurgeon is over age 60. It appears that surgeons chose to have a resection because of the larger volume of the tumor with indentation of the lateral surface of the brain stem. This patient was also a real neurosurgeon who had radiosurgery. He remains well 18 months after the procedure with a decrease in the size of the tumor, and his facial function remains normal.
Some Common Patient Questions
When we evaluate patients with acoustic tumors, many ask the following two questions. First, is the tumor more difficult to resect if radiosurgery fails? The answer to this is not clear. Few patients have required resection after radiosurgery, and the opinions of the surgeons we have asked indicated that some tumors were less difficult, some were about the same, and some were more difficult to resect. In a report on this issue that included thirteen patients who had resection after radiosurgery, eight were thought to be more difficult. However, five of the eight patients had failed resection before they had radiosurgery. In a recent report, Regis et al. noted that most tumors were not more difficult to resect after radiosurgery than the typical untreated tumor.
Second, patients inquire about the risk of delayed malignant transformation. Malignant schwannomas are rare, but have been reported to occur spontaneously, after prior resection, and after irradiation. We answer that delayed malignant transformation is always a risk after irradiation, but the risk should be very low. We have not yet seen this in any of our 6400 patients during our first 17 years of experience with radiosurgery, but quote patients a risk of 1 in 1000 over the next 5–30 years of their life. We believe the risk of developing a tumor years after radiosurgery is much less than the risk of mortality immediately after a resection, and likely less than the risk of the patient developing another tumor on his own in another body location.
Neurofibromatosis Type II
We have conducted detailed evaluations for Gamma Knife radiosurgery in patients with tumors due to neurofibromatosis type II. Imaging studies of 45 tumors over a median 36-month follow-up (range, 6–120 months) found that 16 tumors (36%) had regressed, 28 tumors (62%) remained unchanged in size, and one tumor (2%) demonstrated progression. Loss of central contrast within the tumor was observed in some patients and was thought to reflect tumor necrosis.
At our last detailed review, the mean period of clinical follow-up was 41 months (range, 6–120). Thirty patients (67%) maintained a stable exam and 15 patients (33%) demonstrated some degree of clinical deterioration. Two patients (4%) died during the follow-up period due to unrelated illnesses. The median Karnofsky score after radiosurgery was 80. The Karnofsky score reflects a person's ability to perform common tasks. Thirty-five patients (78%) were able to carry out normal daily activities at the time of the last examination (Karnofsky score =80).
Of the 14 tumors associated with useful hearing (Gardner-Robertson grades 1 or 2) at the time of radiosurgery, six (43%) demonstrated no change in hearing class during the follow-up period.
In tumors managed since 1992, nine patients with useful hearing underwent radiosurgery. Six of the patients (67%) had hearing preservation at the time of last examination. Thirty-one tumors (69%) were associated with intact facial nerve function (House-Brackmann grade 1) at the time of radiosurgery. Three patients (8%) experienced trigeminal distribution sensory loss at a mean five months (range, 4–5 months) after radiosurgery.
Patients with acoustic neuromas have several options available to them. Large tumors with significant brainstem compression usually require surgical resection. For patients with small or medium sized tumors, radiosurgery has become a common treatment with excellent long-term results. Patients must be comfortable with the concept of tumor control rather than tumor removal. Most seem to be satisfied with this concept, if it allows them to avoid brain surgery. Surgeons should strive to educate their patients with information from the peer-reviewed literature. Confusion amongst patients exists because information from Internet sources, newsletters, support groups and physicians has not always been validated and supported by outcomes data. The long-term results of radiosurgery from numerous centers support its important role in the care of patients with appropriate tumors.