Resection of Vestibular Schwannomas with CN VII Posterior to the Tumor: Surgical Techniques and Clinical Outcomes

Introduction: Vestibular schwannomas (VS) are the most common tumor of the cerebellopontine angle. As VSs arise from the vestibular nerve, most displace CN VII anteriorly. An anteriorly displaced CN VII does not obscure access to the presenting pole of the VS via a suboccipital or translabyrinthine approach. Rarely, CN VII is found on the posterior, presenting, surface of the VS—adding difficulty to the surgical resection. We present surgical and clinical results in a series of patients undergoing microsurgery for VS in whom CN VII was displaced posteriorly.

Methods: Retrospective review of a prospectively collected database of VSs undergoing microsurgical resection by the senior authors was performed. Patients with intraoperatively identified, stimulation confirmed, posterior displacement of CN VII were included. Demographic information included sex and age at surgery. Radiographic and clinical variables included largest posterior fossa diameter, Koos grade, prior treatment, and pre and postoperative hearing status and CN VII function. The House-Brackmann (HB) and the American Academy of Otolaryngology – Head and Neck Surgery (AAO–HNS) scales classified CN VII function and hearing levels, respectively. Surgical variables included approach, extent of resection (EOR), and percent change in supramaximal stimulation of CN VII. We provide two illustrative operative videos.

Results: A total of 962 VSs underwent microsurgical resection by the senior authors. Seven patients (0.7%) with posterior displacement of CN VII by their VS were identified. There were 4 males and 3 females with a mean age of 47.8 years (range: 23–66 years). One patient had prior radiosurgery. The mean maximal CPA tumor diameter was 22 mm (range: 19–28 mm). Preoperatively, two patients had AAO–HNS class A hearing, three had class B hearing, and two had class D hearing. All patients were HB grade 1 preoperatively. Six patients underwent a retrosigmoid approach, and one underwent a translabyrinthine approach. Supramaximal stimulation was recorded in six patients, and the mean drop was 32.8% (range: 14–85%) at the conclusion of resection. Gross total resection (GTR) was achieved in two patients, near total resection (NTR) was achieved in three patients, and subtotal resection (STR) was achieved in two patients. Both patients receiving GTR had immediate postoperative HB scores of 6, and both recovered to HB 3- at 12-month follow-up. Among patients undergoing STR or NTR, four had immediate postoperative HB scores of 2, and one had a score of 1. Two patients with STR or NTR had 12-month follow-up, and both improved to HB 1 at follow-up. The eighth nerve was anatomically preserved in two cases. Six patients had AAO-HNS class D hearing postoperatively and one had AAO-HNS class A hearing ([Fig. 1]).

Conclusion: Posterior displacement of CN VII by VSs is a microsurgical challenge requiring alteration of the normal sequence of tumor debulking followed by dissection of the VS-CN VII interface. In these patients, achieving GTR and preserving acceptable CN VII function is challenging. Therefore, we recommend a low threshold for attempting NTR or STR to preserve CN VII function.

Fig. 1

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Artikel online veröffentlicht:
05. Februar 2024