Cystic Vestibular Schwannomas Respond Best to Radiosurgery

BACKGROUND: Vestibular schwannomas (VS) have a well-documented response to Gamma Knife® (Elekta AB, Stockholm, Sweden) Stereotactic radiosurgery (SRS). However, there are limited data available regarding the volumetric response of cystic tumors. OBJECTIVE: This report correlates the radiographic appearance of VS before radiosurgery with the delayed volumetric response. METHODS: This study reviewed our SRS experience with 219 VS patients between 2003 and 2013. Patients were treatment naïve and had a significant extracanalicular tumor volume. Magnetic resonance imaging at the time of SRS identified 42 contrast-enhancing macrocystic tumors, 45 contrast-enhancing microcystic tumors, and 132 homogeneously enhancing tumors with no intratumoral cyst formation. The median follow-up was 49.1 months. The median tumor volume was 2.6 cm 3 (0.70-16.1 cm 3 ) and the median dose was 12.5 Gy (11-13 Gy). RESULTS: The actuarial tumor control rate was 99.4% at 2 years and 96.4% at 5 years. A volumetric reduction of >20% occurred in 85.4% of macrocystic tumors, 76.1% of microcystic tumors, and 62.8% of homogeneously enhancing VS. The median volume decrease per year for macrocystic, microcystic, and homogenous tumors was 17.2%, 7.5%, and 7.9% per year respectively ( P < .001). A 2:1 blinded volumetric case match showed a significant size reduction in macrocystic tumors compared to noncystic tumors ( P = .007). Serviceable hearing was maintained in 61.5% of patients that had Gardner-Robertson grade I-II hearing before treatment. Surgical resection or repeat radiosurgery was performed in 8 patients (3.6%) who had sustained tumor progression. CONCLUSION: SRS provided VS tumor control in >95% of patients, regardless of radiographic characteristics. Tumor volume regression was most evident in patients with cystic tumors.