Outcomes after gamma knife radiosurgery in solitary acoustic tumors and neurofibromatosis Type 2
Surgeons perform stereotactic radiosurgery as the main alternative to acoustic tumor (vestibular schwannoma) resection. The goals of radiosurgery include preservation of neurological function and prevention of tumor growth. Longer-term outcomes are not well documented for patients with solitary tumors or those with neurofibromatosis Type 2 (NF2). To define outcomes, the authors evaluated 462 consecutive patients with solitary acoustic tumors and 40 patients with NF2 (total of 45 tumors treated) who underwent radiosurgery between 1987 and 1998. Serial imaging studies, clinical evaluations, and a patient survey were performed. The average tumor margin dose was 15 Gy, and the mean transverse tumor diameter was 22 mm. In patients with solitary tumors, prior resection had been performed in 111 patients (24%); 27 patients experienced tumor recurrence after a "total resection." The clinical tumor control rate (no resection required) was 98%. In non-NF2 patients followed for at least 5 years, 100 tumors (61.7%) were smaller, 53 (32.7%) remained unchanged in size, and nine (5.6%) were slightly larger. Resection was performed in four patients (2.4%). Neurological deficits after radiosurgery all occurred within the first 28 months. The rates of facial and trigeminal neuropathy varied with radiosurgery technique. In patients with NF2, 16 tumors were smaller, 28 remained unchanged, and one enlarged (overall 98% control rate at median 3-year follow up). Resection was performed in three patients (7%). Useful hearing was preserved in six (43%) of 14 NF2 patients who had useful hearing before radiosurgery. Radiosurgery provided long-term tumor control associated with high rates of neurological function preservation. No further tumor surgery was necessary in 98% of patients with solitary tumors followed for a minimum of 5 years.