Posterior semicircular canal dehiscence: first reported case series.

OBJECTIVE: To identify clinical, audiological, and vestibular characteristics of posterior semicircular canal dehiscence. STUDY
DESIGN: Retrospective case review.
SETTING: Tertiary referral center. PATIENTS: Twelve patients aged 2 to 67 years identified with posterior semicircular canal dehiscence.
INTERVENTIONS: Patients identified by suspicious clinical history and examination, confirmed by high-resolution computed tomography. Audiological evaluation included air and bone audiometry, tympanometry, acoustic reflexes, and vestibular evoked myogenic potential testing.
RESULTS: Hearing loss was mixed in 9 patients, conductive in 2 patients, and sensorineural in 1 patient, with downward-sloping configuration being the most common. Imaging revealed that 7 of 12 patients had dehiscence into a high-riding jugular bulb and 1 patient had an enlarged vestibular aqueduct with a Mondini malformation. One patient had Apert syndrome and another patient had microtia/atresia. Vestibular symptoms were more common in the adult patients than in the pediatric patients, with chronic disequilibrium the most common complaint. Vestibular evoked myogenic potential testing confirmed dehiscence with the characteristic response of reduced threshold and higher amplitude compared with healthy patients.
CONCLUSION: This is the first reported series of adult and pediatric patients with symptomatic posterior semicircular canal dehiscence. Posterior semicircular canal dehiscence represents a third-window lesion manifesting as hearing loss with vestibular dysfunction. Computed tomography findings of a dehiscent posterior canal can be verified with increased vestibular evoked myogenic potential responses as in other third-window lesions. Patients found to have a high-riding jugular bulb and hearing loss should have specific inspection of the posterior canal to ensure it is not dehiscent.