Facial Nerve Outcomes following Adjuvant Gamma Knife Radiosurgery for Subtotally Resected Vestibular Schwannomas: Immediate versus Delayed Timing of Therapy

Background Subtotal resection of vestibular schwannomas (VS) is a valuable surgical approach where gross total resection carries an elevated risk of facial nerve injury. Timing of adjuvant therapy for residual and recurrent VS remains debated, and the effect of gamma knife radiosurgery (GKRS) on facial nerve function following a subtotal resection is incompletely defined.

Methods Clinical and operative records for all patients having undergone a craniotomy for resection of a VS between 1985 and 2017 were reviewed, with cases of subtotal resection identified therein. Facial nerve function was graded according to the House-Brackmann (HB) scale. Doses for all GKRS procedures ranged from 12 to 13 Gy to the 50% isodose line, depending on tumor size. GKRS performed within 12 months of subtotal resection was considered as performed upfront as an adjuvant tumor control strategy. Cases undergoing GKRS greater than 12 months from subtotal resection were identified as observation-first strategy.

Results Craniotomy for subtotal resection of VS was performed in 35 patients to preserve facial nerve function. GKRS was performed upfront for tumor control within 12 months of surgical resection in 11 cases, while the remaining 24 cases underwent observation after surgery. Ultimately, 8/24 (33%) of the observation cases required treatment with GKRS due to recurrent VS growth detected during follow-up surveillance imaging (range: 25−360 months, median 61 months, after surgical resection). In total, 19 patients had GKRS after subtotal resection of a VS. The HB grade for patients having received upfront GKRS remained unchanged in all 11 patients (100%), whereas the HB grade for patients undergoing GKRS for recurrent VS remained unchanged in 7 of 8 patients (87.5%). One patient's facial nerve function deteriorated from HB Grade I to HB Grade III following GKRS performed 109 months after initial surgical resection.

Conclusion Subtotal resection of VS is a prudent strategy, especially when faced with the risk of undue manipulation of neural tissue to achieve a gross total resection. GKRS is safe when performed as an upfront adjuvant therapy for residual tumor burden and appears to carry a low risk of worsening facial nerve function when performed for cases of recurrent disease.