Near and frank dehiscence of the superior semicircular canal: a comparative analysis of clinical outcome.

Objective: Superior canal dehiscence is a pathological aperture of the otic capsule overlying the superior semicircular canal. Currently, two disease subtypes are recognized by experts: frank dehiscence (FD) and near dehiscence (ND). This investigation compares the clinical manifestation and surgical outcomes between patients with FDs and those with NDs, in hopes of delineating their distinctions in pathophysiology and optimal management strategies.

Methods: The authors conducted a cohort study of consecutive middle cranial fossa repairs performed at their institution between 2011 and 2022. FDs were defined as clear dehiscence of the otic capsule, and NDs were defined as focal dehiscence or very thin bony labyrinth (< 0.1 mm) on CT imaging. Multivariable regression models were constructed to assess the relationship of dehiscence subtype with audiometric and symptomatologic baseline presentation and postrepair outcomes. Models were adjusted for demographics, history factors, and follow-up duration.

Results: Among 421 repairs included, 100 (24%) were for NDs and 321 (76%) were for FDs. At 250 Hz, FDs and NDs had a comparable baseline air-bone gap (ABG) (adjusted mean 23.8 dB vs 11.1 dB; adjusted β [aβ] 12.8, 95% CI -0.4 to 25.9) and exhibited a similar degree of narrowing postrepair (-11.7 vs -5.5; aβ -6.2, 95% CI -16.8 to 4.5). At 500 Hz, FDs had a wider baseline ABG (15.4 vs 6.4; aβ 9.1, 95% CI 4.3-13.8) but exhibited numerically greater narrowing postrepair (-6.1 vs 1.1; aβ -7.2, 95% CI -11.4 to -3.0). Despite similar baseline symptomatology, patients with FDs reported lower resolution rates of hearing loss (adjusted OR [aOR] 0.43, 95% CI 0.20-0.94) and higher postoperative onset rates of dizziness (aOR 5.12, 95% CI 1.06-24.76) and vertigo (aOR 8.56, 95% CI 1.11-66.16). Resolution rates for autophony and hyperacusis were similarly high (> 60%) among both cohorts.

Conclusions: Compared to patients with NDs, those with FDs presented with a wider low-frequency ABG but similar symptom profile at baseline. Postsurgery, patients with FDs demonstrated numerically greater ABG narrowing but reported higher rates of dizziness, vertigo, and persistent hearing loss. Nevertheless, surgery yielded objective and subjective benefits among both patients with FDs and those with NDs.