(0605) Air-Bone Gap Closure in Surgical Patients With a Thin Bone Covering the Superior Semicircular Canal

Introduction: Superior Semicircular Canal Dehiscence (SSCD) is a rare defect that can lead to both vestibular and/or auditory symptoms. The syndrome is due to a bony defect within the superior canal, creating a mobile “third window.” Additionally, patients with thin bone covering the semicircular canal, but no full dehiscence, can also present with similar symptoms to patients with true canal dehiscence. Surgical repair to close this defect is usually the most effective method of managing this condition. This study investigates the amount of reduction of the air-bone gap (ABG) in patients with thin bone covering the semicircular canals after surgery.

Methods: A retrospective chart analysis of 58 patients diagnosed with thin bone covering the semicircular canal was conducted in June 2023. Thin bone was defined as patients without true dehiscence with appropriate third window lesion clinical symptomatology. Patients underwent surgical repair in one or both ears. The surgery was conducted with a middle cranial fossa approach in all cases. ABGs were measured across the various frequencies tested. These were compared to the preoperative hearing thresholds.

Results: At 250 Hz, there was a mean reduction in ABG of 2.273 (two-tailed p = 0.05). At all other frequencies analyzed, there was no statistically significant reduction in the ABG before and after surgical correction.

Conclusions: Our results indicate that surgery decreased the ABG in thin bone superior canal patients at 250 Hz. It remains unclear why other frequencies did not have similar reductions in the ABGs.