Long-term Results of Upfront, Single-session Gamma Knife Radiosurgery for Large Cystic Vestibular Schwannomas

Background: Anecdotally, cystic vestibular schwannomas (cVSs) are regarded to have unpredictable biologic activity with poorer clinical results and most studies showed a less favorable prognosis following surgery. While stereotactic radiosurgery (SRS) is a well-established therapeutic option for small to medium-sized VSs, cVSs are often larger, thus making upfront SRS more complicated. The purpose of this retrospective study was to assess the efficacy and safety of upfront SRS for large cVSs. Methods: : The authors reviewed the data of 54 patients who received upfront, single-session GKRS with a diagnosis of large cVS (>4 cm3). Patients with neurofibromatosis type 2, multiple VSs, or recurrent VSs and < 24 months of clinical and neuroimaging follow-up were excluded. Results: : Hearing loss (48.1%) was the primary presenting symptom. The majority of cVSs were KOOS grade IV (66.7%), and the most prevalent cyst pattern was “mixed pattern of small and big cysts” (46.3%). The median time between diagnosis and GKRS was 12 months (range, 1-147 months). At GKRS, the median cVS volume was 6.95 cm 3 (range, 4.1–22 cm 3 ). The median marginal dose was 12 Gy (range, 10-12 Gy). The mean radiological and clinical follow-up periods were 62.2 ± 34.04 months (range, 24-169 months) and 94.9 ± 45.41 months (range, 24-175 months), respectively. At 2, 6, and 12 years, the tumor control rates were 100%, 95.7%, and 85.0%, respectively. Tumor shrinkage occurred in 92.6% of patients (n=50), tumor volume remained stable in 5.6% of patients (n=3), and tumor growth occurred in 1.9 percent of patients (n=1). At a median follow-up of 53.5 months, the pre-GKRS tumor volume significantly decreased to 2.35 cm3 (p<0.001). While Koos grade 3 patients had a greater possibility of attaining higher volume reduction, “multiple small thick-walled cyst pattern” and smaller tumor volumes decreased the likelihood of achieving higher volume reduction. Serviceable hearing (Gardner-Robertson Scale I-II) was present in 16.7% of patients prior to GKRS and it was preserved in all of these patients following GKRS. After GKRS, 1.9% of patients (n=1) had new-onset trigeminal neuralgia. There was no new-onset facial palsy, hemifacial spasm, or hydrocephalus. Conclusions: : Contrary to what was believed, our findings suggest that upfront GKRS seems to be a safe and effective treatment option for large cVSs.