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

ABSTRACT

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.