Facial Nerve Outcome and Extent of Resection in Cystic versus Solid Vestibular Schwannomas in Radiosurgery Era: Is Near-Perfect Possible?

Objective Vestibular schwannomas (VS) are benign, slow-growing tumors accounting for 8 to 10% of all primary intracranial tumors. The reported incidence of cystic VS (CVS) which are associated with unpredictable clinical behavior as well as unfavorable postoperative outcomes is between 4 and 48%. We aimed to review our experience in microsurgical treatment of CVS particularly in terms of extend of resection and postoperative facial nerve (FN) outcomes in comparison with their solid counterparts.

Methods Two hundred and eleven patients with the diagnosis of VS were managed surgically between January 2006 and June 2017. Tumors were defined as cystic when preoperative neuroimaging demonstrated cyst formation which is confirmed by intraoperative findings. Solid VS (SVS) with similar extension grades (Hannover classification) were used for comparison. Patients who had bilateral VS, the diagnosis of neurofibromatosis or Grade I and II solid tumors, were excluded. Thirty-five CVS and 53 SVS matching the inclusion criteria were identified. Clinical data of the patients were reviewed retrospectively, including preoperative and postoperative notes, operative reports, pathology reports, images, and neuroradiology reports.

Results A total of 34 patients (male = 20, female = 14) with a mean age of 52.1 years (range: 17–77 years) underwent microsurgical resection for 35 CVSs. All CVSs were Grade III or IV with a mean size of 3.2 cm (range: 1.5–5 cm). All operations except the three requiring staged resections were performed in a single session via either of retrosigmoid (n = 7, 20.58%) or translabyrinthine approach (n = 25, 73.52%). Gross total resection (GTR) was achieved in 30 of CVSs (88.24%) and 41 of SVSs (77.36%). Subtotal resection (STR) was possible in two (5.88%) and seven (13.21%) of CVSs and SVSs, respectively. Near-total resection (NTR) was achieved in two patients (5.88%) with CVS and five (9.43%) patients with SVS. The main reason for STR and NTR was adherence of the tumor to brainstem and/or FN in both groups. Recurrence was observed in one of the patients with CVS (2.94%) 8 years after GTR and required reoperation. None of the four patients with STR or NTR in this group demonstrated symptomatic regrowth of the tumor so far. FN was anatomically preserved in all patients in both groups. Favorable FN outcomes were achieved in 22 of CVS surgeries (62.86%) and 42 of SVS surgeries (79.24%) at the time of discharge. Among the patients reaching the 1-year follow-up, favorable FN outcomes were noted following 27 (96.43%) of CVS surgeries and 47 (97.91%) of SVS patients, respectively. None of the patients died following VS surgery.

Conclusion Preservation of FN functions is one of the major goals of VS surgery, while complete resection of the tumor is another. Besides, surgery of CVS does not necessarily result in worse surgical outcomes in terms of GTR and favorable FN function rates. Particular attention should be paid to preserve anatomic continuity of the FN during surgery since when uninterrupted, long-term FN functions are much more satisfactory in comparison with early postoperative results. Moreover, GTR or NTR seems a highly feasible consequence in CVS surgery especially in experienced hands.