Residual Vestibular Schwannomas: Proposed Age-Tumor-Residual (ATR) Staging System to Predict Future Growth.

Objective: To assess growth rates of residual vestibular schwannoma after subtotal and near-total surgical resection and establishing staging system for risk of residual tumor growth.

Study Design: Retrospective cohort study.

Setting: Tertiary referral center.

Patients: Patients with residual vestibular schwannoma after surgical resection from 2011 to 2023 identified on postoperative MRI defined as near-total resection (NTR, less than 5 mm of remaining tumor), subtotal resection (STR; 5-10 mm) and debulking (>10 mm).

Main Outcome Measures: Tumor growth of 2 mm or more after subtotal or near-total surgical resection of vestibular schwannoma.

Results: A total of 56 patients (54% female; mean, standard deviation [SD] age 51 [17] yr) had residual tumor. Mean preoperative tumor size was 3.0 (1.1) cm, and residual tumors involved both sides with similar frequency (right: 52%). Quantitatively, 29% were NTR, 32% were STR, and 39% were debulking. With an average follow-up of 27 (SD 31) months, tumor growth occurred in 11 (20%), tumor shrinkage occurred in 16 (29%), and tumors were unchanged in 29 (51%) cases. Growing residual tumors were treated with radiation (7 patients) or a second surgical resection (4 patients). Multivariable analysis identified lower patient age, larger preoperative tumor size, and larger residual tumor size in risk of residual growth. A residual VS tumor staging system (Age, Tumor, Residual [ATR]) is proposed with most tumors in stage II (22, 42%) or stage III (23, 44%), whereas 7 (14%) tumors are stage I.

Conclusions: Approximately 80% of residual VS are stable or shrink in size. Initial observation is advocated after incomplete resection and long-term follow up is needed. Patient age less than 55 years, larger preoperative tumor size, and larger postoperative residual tumor size appear predictive of residual tumor growth.Level of Evidence: 4.