Natural History of Growing Sporadic Vestibular Schwannomas: An Argument for Continued Observation Despite Documented Growth in Select Cases

Objective: Definitive treatment of sporadic vestibular schwannoma (VS) following documented growth is common practice at most centers in the United States. However, as a natural extension of this paradigm, very little evidence exists surrounding the natural history of growing tumors. The primary objective of the current work was to describe the natural history of sporadic VS following documentation of initial tumor growth. Study Design: Retrospective cohort study. Setting: Tertiary referral center. Patients: Patients diagnosed with sporadic VS between January 1, 2001 and December 31, 2015 who elected continued observation despite having volumetric growth >= 20% of original tumor volume on interval magnetic resonance imaging (MRI). Main Outcome Measure: Survival free of subsequent volumetric growth. Results: Of 361 patients undergoing observation with serial imaging during the study period, 85 patients met inclusion criteria at a median age of 66 years (interquartile ranges [IQR] 55-71). Within this cohort, 40 patients demonstrated subsequent volumetric growth at a median of 1.7 years (IQR 1.0-2.6) from the date of initial MRI that documented growth. The median volumetric growth was 43% (IQR 28-57), and the median growth rate was 0.026 cm(3) per year (IQR 0.009-0.107). Survival free of subsequent volumetric growth rates (95% CI; number still at risk) at 1, 2, 3, 4, and 5 years were 93% (87-99; 75), 67% (58-79; 45), 54% (43-67; 29), 44% (33-59; 19), and 41% (30-56; 12), respectively. Conclusions: In a cohort exclusively comprised of sporadic VS with documented growth, over 40% of tumors demonstrated no subsequent volumetric growth after 5 years of continued MRI surveillance. These data challenge the supposition that once growth occurs, all tumors will exhibit sustained growth. Continued observation after documented growth of sporadic VS is a reasonable consideration in appropriately selected cases.