Delayed Vestibular Schwannoma Growth following Steretoatactic Radiosurgery

Vestibular Schwannomas have unpredictable growth patterns. Stereotactic RadioSurgery (SRS) is a well recognized treatment for Vestibular Schwannomas (VS). Previous studies have shown positive outcomes from SRS with the growth of most tumors being well controlled. Long term outcomes however remain uncertain. The aim of this study was to examine for any patients with a VS which initially regressed or stopped growing post SRS and then starting growing again after an interval period.

A retrospective analysis of all patients with VS managed in a tertiary referral center was performed. The computerised Radiology imaging System was used to analyze the Magnetic Resonanc Imaging(MRI) of all patients. The tumor volume was calculated by measuring the 3 planes on axial and coronal contrast-T1-weighted MRI. Significant change in size was deemed as greater than 15%. Patients with NF2 or where the MRI images were not available were excluded.

In a 10 year period 495 patients with VS were identified. Eighty three patients with unilateral large or growing VS or where there were other concerns received SRS. Fifty percent showed evidence of growth in the first post treatment scan (6–12months) post SRS. Fifty-five percent of all those treated then showed evidence of regression in 2 years follow up. Two patients were found to have a VS which exhibited growth in the first post treatment scan and then regression (although not to a size less than the pre-treatment size), then after a 3 and 4 year interval showed further evidence of growth.

Our results show a trend for a decrease in tumor size in long term follow up for most patients receiving SRS, however on occasions tumors that show some regresion can start growing again. This study highlights the need to keep patients under long term review with serial imaging post SRS.