Superior semicircular canal dehiscence isolation by transmastoid two-point canal plugging with preservation of the vestibulo-ocular reflex.

This article describes the surgical treatment of superior semicircular canal dehiscence syndrome (SCDS) by isolating the dehiscence using transmastoid two-point canal plugging while preserving the high-frequency vestibulo-ocular reflex (VOR) of the affected semicircular canal. The superior semicircular canal is opened via a transmastoid approach anterior (as far from the ampulla as possible) and posterior to the dehiscence and then plugged with connective tissue and bone dust. In two clinical exemplary cases, vestibular testing showed that the VOR measured by video head impulse (vHIT) test was preserved (patient 1: gain preoperative 0.7, long-term postoperative 0.75; patient 2: gain preoperative 0.64, long-term postoperative 0.79; reduction of corrective saccades in each case) with a simultaneous reduction in pathologically increased amplitudes of vestibular evoked myogenic potentials (VEMPs) and a significant improvement in clinical symptoms with almost complete freedom from symptoms. One possible explanation for preservation of the high-frequency VOR of the superior semicircular canal would be the deformability of the endolymphatic space described at high stimulation frequencies, which can lead to endolymph movements in the area of the ampulla with deflection of the cupula despite blockage of the semicircular canal.