Differential Responses to Early versus Delayed Stereotactic Radiosurgery for Subtotally Resected Vestibular Schwannoma

Introduction: Decision making in vestibular schwannoma (VS) management is nuanced and polyfactorial, with many clinical inflexion points lacking strong evidence to guide care. In the postoperative setting, extent-of-resection is the most important predictor of long-term tumor control, with recurrence rates reported from < 1 to 9% after gross-total resection (GTR), versus up to 44% after subtotal resection (STR). Correspondingly, many VS are considered for stereotactic radiosurgery (SRS) after STR, but optimal timing remains unclear, and various authors advocate for early adjuvant treatment to improve tumor control, versus delayed treatment at the time of recurrence/progression to minimize potentially unnecessary radiation exposure. We report our experience with SRS after STR in a population of radiation-naive VS, and compare outcomes between patients who underwent adjuvant versus delayed treatment.

Methods: STR patients were identified and primary data capture was completed by retrospectively querying a prospectively maintained institutional VS database. In addition to baseline demographics, clinical and radiographic data were abstracted at preoperative, postoperative, time-of-SRS, and last follow-up; endpoints included tumor volume, AAO-HNSF hearing class, House–Brackmann facial nerve function, SRS treatment parameters, and postoperative/post-SRS complications.

Results: Fifteen patients without a history of radiation, multiple VS resections, or facial reanimation were treated with SRS after STR during 2002–2017, and therefore met criteria for study inclusion. Eleven were female (73%), overall median age was 51 at first operation (range: 15–73), and 9 VS were left-sided (60%). Class A/B absent in all patients by time-of-SRS. Favorable House–Brackmann Grades I to II facial nerve function was present in all patients prior to surgery, and preserved at time-of-SRS in 10 (67%). No patient had worsened facial nerve function after SRS, and as of last follow-up, two had recovered from Grade VI to Grade III, and two had recovered from Grade III/IV to Grade I.

Five patients were treated with up-front adjuvant SRS ∼1 year after surgery (33%), while 10 were treated at the time of progression (66%), a median 42 months postoperatively (range: 23–98). As of last follow-up, 14 patients demonstrated durable tumor control at a median 43 months post-SRS (range: 25–104), while 1 patient from the delayed treatment group failed SRS and required repeat resection (7% vs. 0%, p = 1.0). Dosimetry parameters were similar between the groups with a median margin dose of 13 Gy and a median maximum dose of 26 Gy for the overall, early, and delayed groups. Differences in overall facial nerve or hearing outcomes were not significant. Transient hemifacial spasm developed in 3 patients each, a difference that was not significant (p = 0.33). Total follow-up was a median 85 months from primary resection (range: 37–136). No patients developed a secondary malignancy, and there were no deaths.

Conclusion: VS management after STR is challenging, and optimal timing of SRS remains unresolved. At present, we recommend tailoring treatments to the needs of the patient. For most individuals, delayed SRS is an appropriate option that likely reduces radiation exposure and cost without significant risk of eventual treatment failure; notwithstanding, in patients whose tumors had grown rapidly preoperatively, early adjuvant SRS remains a reasonable consideration.

No conflict of interest has been declared by the author(s).