Length of Tumor-Cochlear Nerve Contact and Hearing Outcome after Surgery for Vestibular Schwannoma

Introduction: Tumor size is considered an important variable that probably impacts the likelihood of hearing preservation after surgery for vestibular schwannoma. However, some large series have not supported this concept, possibly due to variation in the technique used for tumor measurement. We sought to determine if the length of tumor-cochlear nerve contact was predictive of hearing outcome in adult patients undergoing resection of pathologically confirmed vestibular schwannoma.

Methods: Patients who underwent a hearing-preserving approach for resection of a vestibular schwannoma at one institution by a neurosurgeon/neurotologist team between 2001 and 2005 were screened. Patients with AAO-HNS class A or B hearing preoperatively were included. MRI scans were reviewed and used to calculate the length of tumor-cochlear nerve contact, the diameter of the extracanalicular component of the tumor, and the length of the intracanalicular component.

Results: Thirty-three patients were included, of whom 9 (27%) had hearing preservation. Length of tumor-cochlear nerve contact was significantly greater (p = 0.041) in those who lost hearing (27.7 mm, 95% CI 23.8 mm–31.6 mm) compared with those who did not (20.7 mm, 95% CI 15.8 mm–25.6 mm). The diameter of the extracanalicular component was similarly significantly greater (p = 0.029, 20.3 mm [15.8 mm–24.8 mm] vs. 12.6 mm [7.9 mm–12.9 mm]).

Conclusion: Vestibular schwannomas with greater lengths of tumor-cochlear nerve contact are at increased risk for hearing loss after attempting hearing-preservation surgery. Increased extracanalicular diameters also place patients at greater risk, a finding consistent with previous studies.