Delayed Tumor Growth in Vestibular Schwannoma: An Argument for Lifelong Surveillance

Objective: Previous research has shown that tumor growth during observation of small-to-medium sized sporadic vestibular schwannomas (VSs) occurs almost exclusively within 3 to 5 years following diagnosis. This has led some to consider ending surveillance after this interval. This study seeks to characterize a cohort of patients with tumors that exhibited late growth. Study Design: Retrospective cohort study. Setting: Tertiary referral center. Patients: Adults with sporadic VSs who initially elected observation with serial magnetic resonance imaging (MRI) surveillance. Intervention(s): None. Main Outcome Measure(s): Linear tumor growth was measured in accordance with AAO-HNS reporting guidelines. Delayed growth was defined as growth ≥2 mm in linear diameter that was first detected 5 years or more from the initial MRI. Results: From a total of 361 patients, 172 experienced tumor growth during the interval of observation. Fourteen of these 172 patients (8.1%) experienced late growth occurring at 5 years or beyond. Among patients with delayed growth, the fastest growth rate after extended quiescence was 1.33 mm/yr, and the longest delay before tumor growth detection was 11.1 years. Additional treatment was recommended for six (42.9%) of the patients with delayed growth. Of 68 tumors that remained in the IAC, 11 (16.2%) demonstrated delayed growth. Of 66 tumors that presented in the CPA, 2 (3.0%) demonstrated delayed growth. Initial size was larger for tumors demonstrating early growth compared with those with delayed growth. For tumors within the IAC, those with early growth had a significantly higher median growth rate than those with delayed growth (1.40 vs. 0.45 mm/yr, p < 0.001). Conclusions: Delayed growth encompassed 8.1% of growing VSs and 3.9% of all observed tumors. Patients with delayed growth exhibited slower growth rates compared with those who were diagnosed with growth early in their observation course. These findings support the need for lifelong surveillance of untreated VSs given the possibility of clinically significant delayed growth. Increasing the time interval between MRI studies after 5 years is a reasonable concession to balance practicalities of cost and convenience with risk of delayed of tumor growth.