Near-dehiscence: Clinical findings in patients with thin bone over the superior semicircular canal

Objective: To determine whether patients with thin bone over the superior semicircular canal can develop signs or symptoms of superior canal dehiscence syndrome (SCDS). Study Design: Retrospective case series. Setting: Tertiary referral center. Patients: All patients from our institution found to have thin but not frankly dehiscent bone over the superior canal despite symptoms and signs of SCDS. Main Outcome Measures: Preoperative CT imaging, symptoms, audiometry, vestibular evoked myogenic potentials (VEMP), and intraoperative electrocochleography (ECochG) results were reviewed. Symptoms were assessed at least 1 month postoperatively in all patients, and postoperative physiologic data are presented when available. Results: Ten patients (11 ears) had thin bone over the superior semicircular canal at surgery. All presented with autophony or sound- and/or pressure-induced vertigo, in addition to at least 1 physiologic measure consistent with SCDS. CT imaging was read as showing either dehiscence (36%) or marked thinning of bone overlying the affected canal (64%). Preoperative median low-frequency air-bone gap (ABG) was elevated (10.9 dB; interquartile range [IQR], 8.8-12.5), with 4 patients demonstrating negative bone conduction thresholds. Patients had elevated oVEMP amplitude (median, 20.7; IQR, 6.7-22.1) μV and ECochG SP/AP ratios (median, 0.59; IQR, 0.54-0.67). Postoperative ABG and SP/AP ratio decreased significantly compared with preoperative values (p < 0.05), and all patients reported symptomatic improvement. Conclusion: Symptoms typical of SCDS can occur in cases with thin but not dehiscent bone. Surgical plugging or resurfacing can reduce symptoms in such cases.