BACKGROUND: Superior semicircular canal dehiscence syndrome (SCDS) produces a wide spectrum of vestibular and auditory abnormalities due to the presence of a "third mobile window." While enhanced otolith-mediated responses are well recognized, the behavior of high-frequency semicircular canal function remains debated. Many patients show reduced superior canal vestibulo-oculomotor reflex (VOR) gains despite preserved or exaggerated utricular responses. OBJECTIVE: To investigate the relationship between dynamic semicircular canal responses assessed by video Head Impulse Test (vHIT) and otolith responses assessed by oVEMPs in people with superior semicircular canal dehiscence. METHODS: Fifty-three patients with SCDS underwent full vestibular testing including vHIT of all six semicircular canals, cervical and ocular vestibular-evoked myogenic potentials (cVEMPs, oVEMPs) to 500-Hz BCV, and high-frequency oVEMPs to 4,000-Hz stimuli. RESULTS: Superior semicircular canals showed the largest VOR gain reductions, with the left anterior (LA) canal most affected (mean gain 0.86 ± 0.18). Bilateral SCDS exhibited significantly lower gains than unilateral SCDS, with mean LA gain falling below the functional threshold (0.68 ± 0.14). In contrast, all patients demonstrated enhanced utricular responsiveness, including increased 500-Hz oVEMP amplitudes and consistent 4-kHz N10 responses. CONCLUSION: Our findings confirm the presence of high-frequency oVEMP hyperresponsiveness, yet with a VOR pseudo-hypofunction due to a loss of high-frequency mechanical energy through the dehiscence, which diminishes the utricular vortex and cupular deformation. This frequency-dependent hydrodynamic dissociation provides a comprehensive mechanistic framework for interpreting vestibular test batteries in SCDS. Combined assessment with vHIT and high-frequency oVEMPs offers a powerful, physiologically grounded diagnostic approach.
Manzari et al. (Mon,) studied this question.