Outcomes of Fractionated Radiosurgery in Cystic Vestibular Schwannoma

Abstract

Evaluate outcomes of fractionated SRS in predominantly cystic vestibular schwannoma. Patients undergoing fractionated Radiosurgery for VS were retrospectively reviewed. Patients with cystic tumors were considered candidates for SRS only if they did not have symptomatic or significant radiologic brainstem compression. VSs containing dominant intra-tumoral or peri-tumoral cyst(s) > 50% of the total tumor diameter by greatest linear axial CPA dimension, single or multicystic, were included for study. Pre-treatment clinical and radiographic features, including AAO-HNS hearing class, history of facial weakness, current facial and trigeminal nerve function, AAO-HNS tumor size, and intratumoral vs peritumoral cysts were captured. All Patients underwent treatment on C-Arm Linac with CBCT image guidance to a dose of 25gy/5#. Patients underwent MRI surveillance every 6 months for the first year, annually thereafter for the subsequent 2 years, and then every other year. 15 patients (12 women; median age at treatment, 53 years; range, 36-85 years) with cystic VS met inclusion criteria. The median radiologic follow-up within the cystic group was 48 months (range, 17-100 months), and the median change in tumor size was − 4.3mm. 12 tumors (80%) shrank, 2 (13%) remained stable (experienced significant cyst enlargement within 1 year after treatment, followed by spontaneous cyst shrinkage back to the original pretreatment size), and 1 patient (7%) experienced cyst enlargement of 9 mm over 21 months and underwent retrolabyrinthine subtotal tumor removal and cyst decompression enlarged. Tumor control rate in cystic group of 93%. The median radiologic follow-up in the non-cystic control group, comprising of 53 pts. was 67 months (range, 6-141 months), and the median change in size was −2.0 mm. Tumor control in the solid group was 94%. Comparing only those tumors that decreased in size showed that there was a trend toward a greater reduction within the cystic group, intratumoral being better than peri-tumoral cystic VSs (P = .05). The present study demonstrates that tumor control after fractionated SRS for dominant intratumoral cystic VS may not differ from that of noncystic VS in properly selected cases suggesting that intratumoral cysts have a different behavior compared with those with peripheral cystic components, latter may result from trapped arachnoid or a hemorrhage-related process making them, thus, more susceptible to growth despite control of the solid portion of the tumor.