Extent of resection and progression-free survival in vestibular schwannoma: a volumetric analysis

OBJECTIVE To preserve facial nerve function in vestibular schwannoma (VS) microsurgery, some have advocated subtotal resection (STR) if the tumor is densely adherent to a thinned facial nerve. The objective of this study was to determine if residual volume is associated with progression and whether there is a threshold residual volume that should be pursued during STR to prevent recurrence. A secondary objective of this study was to determine whether facial nerve function at last follow-up was associated with extent of resection (EOR). METHODS Clinical and radiographic data were retrospectively collected from the records of 164 patients with VS who underwent resection. Tumor volumes were measured using Visage, and standard statistical methods were used. The House-Brackmann scale was used to assess changes in facial nerve function before surgery and at last follow-up. RESULTS Sixty-one patients (37%) received gross-total resection (GTR) and 103 (63%) received STR. The median clinical and radiographic follow-ups were 49 and 48 months, respectively. The median residual volume was 0.5 cm 3 after STR. Kaplan-Meier actuarial survival analysis revealed a 96.3% 5-year progression-free survival (PFS) rate after GTR, which was greater than that after STR (84.5%, p = 0.03). Recursive partitioning analysis of patients receiving STR revealed a residual volume of 0.60 cm 3 as the optimal threshold for recurrence. Patients with residual volume ≥ 0.60 cm 3 had a 76.0% 5-year PFS, regardless of adjuvant SRS, which was lower than that for patients undergoing GTR (96.3%) or STR (95.6%) with residual volumes < 0.60 cm 3 (p < 0.01). On Cox regression analysis, residual volume ≥ 0.60 cm 3 (HR 14.4, p = 0.01) was independently associated with progression, even when accounting for patient age, adjuvant radiosurgery, and preoperative tumor size. In 112 patients with at least 24 months of follow-up after their last treatment, tumor control was achieved in 111 (99.1%) patients at a median last follow-up of 71 months. Worse facial nerve function at the last follow-up was independently associated with prior treatment for VS (adjusted OR 3.7, p = 0.04), but not residual volume cohort or preoperative tumor volume. CONCLUSIONS Residual volume > 0.60 cm 3 after VS resection was independently associated with tumor progression, even accounting for adjuvant SRS. These data support maximizing the EOR during VS surgery, even if GTR cannot be safely achieved.