Electrocochleography as a Diagnostic and Intraoperative Adjunct in Superior Semicircular Canal Dehiscence Syndrome

Abstract

To determine the electrocochleographic characteristics of ears with superior semicircular canal dehiscence (SSCD) and to examine its use for intraoperative monitoring in canal occlusion procedures. Case series. Academic medical center. Thirty-three patients (45 ears) had clinical and computed tomographic evidence of SSCD; 8 patients underwent intraoperative electrocochleography (ECoG) during superior canal occlusion; 9 patients underwent postoperative ECoG after SSCD occlusion. Diagnostic, intraoperative, and postoperative extratympanic ECoG; middle fossa or transmastoid occlusion of the superior semicircular canal. Summating potential (SP) to action potential (AP) ratio, as measured by ECoG, and alterations in SP/AP during canal exposure and occlusion. Using computed tomography as the standard, elevation of SP/AP on ECoG demonstrated 89% sensitivity and 70% specificity for SSCD. The mean SP/AP ratio among ears with SSCD was significantly higher than that among unaffected ears (0.62 versus 0.29, p < 0.0001). During occlusion procedures, SP/AP increased on exposure of the canal lumen (mean change ± standard deviation, 0.48 ± 0.30). After occlusion, SP/AP dropped below the intraoperative baseline in most cases (mean change, -0.23 ± 0.52). All patients experienced symptomatic improvement. All patients who underwent postoperative ECoG 1 to 3 months after SSCD repair maintained SP/AP of 0.4 or lesser. These findings expand the differential diagnosis of abnormal ECoG. In conjunction with clinical findings, ECoG may support a clinical diagnosis of SSCD. Intraoperative ECoG facilitates dehiscence documentation and allows the surgeon to confirm satisfactory canal occlusion.