Surveillance after resection of vestibular schwannoma: measurement techniques and predictors of growth.

OBJECTIVES To compare different methods of measuring tumor growth after resection of vestibular schwannoma and to identify predictors of growth. STUDY DESIGN Retrospective case review. SETTING Tertiary referral center, inpatient surgery with ambulatory follow-up. PATIENTS All patients who underwent vestibular schwannoma resection by the senior author from September 1991 to April 2012 and had two or more postoperative MRI scans. INTERVENTIONS Vestibular schwannoma resection. Measurement of tumor size and enhancement pattern on postoperative magnetic resonance imaging scans. MAIN OUTCOME MEASURES Tumor size as measured in one (linear), two (planar), and three (volumetric) dimensions using standard radiology workstation tools versus time elapsed since surgical resection. RESULTS Eighty-eight patients were included with mean follow-up of 3.9 years. Linear measurement of tumor size was found to have modest correlation with planar and volumetric measurements. Excellent correlation was found between the planar and volumetric methods. Nodular enhancement increased risk for tumor growth (OR 6.25, p = 0.03 on planar analysis). If there was growth, tumors with nodular enhancement typically showed increase in size beginning 2 years postoperatively, whereas those with linear or no enhancement were typically stable in size through 5 years. Younger age and larger preoperative tumor size were also risk factors for growth (OR 0.9/p = 0.01 and OR 1.09/p = 0.02). CONCLUSION Simple planar measurement is an efficient method that correlates well with the more time-consuming volumetric method. The major risk factor for tumor growth is nodular enhancement on a baseline scan, a finding that warrants annual MRI beginning 2 years postoperatively. Younger age and larger preoperative size minimally increased risk of growth.