Natural History of Growing Sporadic Vestibular Schwannomas During Observation: An International Multi-Institutional Study

OBJECTIVE: Active treatment of small- or medium-sized vestibular schwannoma during wait-and-scan management is currently recommended at most centers globally once growth is detected. The primary aim of the current study was to characterize the natural history of growing sporadic vestibular schwannoma during observation. STUDY DESIGN: Cohort study. SETTING: Four tertiary referral centers across the United States and Denmark. PATIENTS: Patients with two prior MRI scans demonstrating ≥2 mm of linear growth who continued observational management. INTERVENTION: Observation with serial imaging. MAIN OUTCOME MEASURE: Subsequent linear growth-free survival (i.e., an additional ≥2 mm of growth) following initial growth of ≥2 mm from tumor size at diagnosis. RESULTS: Among 3,402 patients undergoing observation, 592 met inclusion criteria. Median age at initial growth was 66 years (IQR 59-73) for intracanalicular tumors (N = 65) and 62 years (IQR 54-70) for tumors with cerebellopontine angle extension (N = 527). The median duration of MRI surveillance following initial detection of tumor growth was 5.2 years (IQR 2.4-6.9) for intracanalicular tumors and 1.0 year (IQR 1.0-3.3) for cerebellopontine angle tumors. For intracanalicular tumors, subsequent growth-free survival rates (95% CI; number still at risk) at 1, 2, 3, 4, and 5 years following the initial MRI that demonstrated growth were 77% (67-88; 49), 53% (42-67; 31), 46% (35-60; 23), 34% (24-49; 17), and 32% (22-47; 13), respectively. For cerebellopontine angle tumors, subsequent growth-free survival rates were 72% (68-76; 450), 47% (42-52; 258), 32% (28-38; 139), 26% (21-31; 82), and 22% (18-28; 57), respectively. For every 1 mm increase in magnitude of growth from diagnosis to tumor size at detection of initial growth, the HRs associated with subsequent growth were 1.64 (95% CI 1.25-2.15; p < 0.001) for intracanalicular tumors and 1.08 (95% CI 1.01-1.15; p = 0.02) for cerebellopontine angle tumors. CONCLUSIONS: Growth detected during observation does not necessarily portend future growth, especially for slowly growing tumors. Because early treatment does not confer improved long-term quality of life outcomes, toleration of some growth during observation is justifiable in appropriately selected cases.