Long-term outcome of Gamma Knife radiosurgery in patients with tiny intracanalicular vestibular schwannomas detected by three-dimensional fast imaging employing steady-state acquisition magnetic resonance

Abstract

ObjectiveTo evaluate the effectiveness and long-term outcome of Gamma Knife radiosurgery (GKRS) for tiny vestibular schwannomas (VSs) detected by three-dimensional fast imaging employing steady-state acquisition magnetic resonance (3D-FIESTA MR). Materials and methodsBetween January and December 2004, 3D-FIESTA MR of the brain was performed in patients who had physical health examinations at the Buddhist Tzu Chi General Hospital (Hualien, Taiwan). Tiny intracanalicular VSs (defined as a tumor volume < 0.5 cm2) was detected in 13 patients (8 women and 5 men). The mean age of the patients was 60 years (range, 45–84 years). Hearing function was graded using the Gardner–Robertson (GR) classification. Dose planning was performed on intraoperative stereotactic contrast-enhanced images using multiple 4-mm isocenters. The mean tumor volume was 0.098 cm2 (range, 0.013–0.4 cm2). The mean margin dose was 12.4 Gy (range, 11–14 Gy), and the isodose line was set at a mean of 53.8% (range, 50–70%). ResultsTwelve patients had GR Grade I or II hearing before GKRS, and GR I or II hearing was maintained in 11 patients. Facial and trigeminal nerve functions were preserved in all patients. The tumor control rate was 100% at a mean follow-up period of 9.8 ± 1.1 years (range, 76–126 months). One patient developed acute vertigo 1 day after GKRS, which subsided after short-term use of steroids and did not recur. ConclusionWith the application of 3D-FIESTA, tiny VSs can be detected early. Because low-dose (12–14 Gy) GKRS is safe and effective for long-term control of the growth of tumors with acceptable preservation rate of hearing function, it may be worthwhile to use 3D-FIESTA to detect tiny VSs and treat the patients using GKRS.