Imaging Post Stereotactic Radiosurgery for Vestibular Schwannomas-When Should We Scan?

Objective To identify the optimal time for imaging following stereotactic radiosurgery (SRS) in patients with vestibular schwannomas (VS). Study design Retrospective case series. Setting Tertiary, university center. Patients Patients with VS treated with SRS. Interventions Pre- and post-SRS surveillance with magnetic resonance imaging (MRI); patients should have at least two pre- and two post-SRS scans available to be included. Main outcome measures Patient demographics, tumor size, and growth per month ratio pre- and post-SRS and time interval between serial MRI. Results Forty-two patients fulfilled the inclusion criteria. The average tumor size before the treatment was 16.9 mm (range, 10-28 mm) while 2 years posttreatment it was 16 mm (range, 7-25 mm) (p = 0.5). Average time of the first MRI post-SRS was 11 months (range, 5-14) with an average change in tumor size at that time of +0.53 mm (range, -5-8). Average time to second MRI was 22.3 months (range, 12-33) with an average change in tumor size at second scan of -1.14 (range, -5-2) mm (p = 0.117). The average growth/mo ratio before SRS was 0.26 mm/mo (range, 0-1), while post-SRS 0.05 mm/mo (range, -0.3-0.5) and -0.16 mm/mo (range, -18-0.25) at the time of the first and second scan, respectively (p Conclusions Given the initial increase in size following SRS, unless clinically indicated, MRI post-SRS at less than 1 year has no clinical value. The growth per month ratio provides more meaningful values for response to treatment than tumor size measurements.