Objective: To describe the underrecognized inner ear malformation characterized by complete aplasia of the labyrinthine semicircular canals associated with a relatively well-formed cochlea, to investigate its relationship with known syndromic forms of hearing loss, and to hypothesize regarding the potential embryopathogenesis of this anomaly.
Study design: A retrospective case review consisting of cases of sensorineural hearing loss with radiographic evidence demonstrating agenesis of the semicircular canals associated with a cochlea that was either morphologically normal or sufficiently well developed to accommodate the full insertion of a cochlear implant electrode. Cases were identified by computerized tomography findings that identified the anomaly under study.
Setting: Departments of otolaryngology and radiology in a tertiary referral center, with a large cochlear implant program serving over 800 patients, more than half of whom are children.
Patients: Fifteen patients with the anomaly under study were identified.
Interventions: Each patient underwent a complete otologic examination, audiometric studies, and high resolution computerized tomography of the temporal bone in axial and coronal planes.
Main outcome measures: The bony morphology of the cochlea, round and oval windows, vestibule, semicircular canals, and vestibular aqueduct, and the course of the facial nerve were examined. Auditory findings and otologic treatment are presented.
Results: Of the 15 identified patients, 4 were nonsyndromic, 9 had CHARGE association (Coloboma of the eye, congenital Heart defects, choanal Atresia, mental and/or growth Retardation, Genital hypoplasia, and Ear anomalies and/or deafness), 1 met criteria for Noonan's syndrome, and one had features of both these syndromes. Although the cochlea was present in all cases, the cochlear morphology was usually abnormal in the CHARGE association patients. Of the 20 ears in the CHARGE subjects, only 3 ears (15%) were seen to have completely normal development of the cochlea in both the basal and upper turns. The others showed either mild hypoplasia of the upper turns (13 ears, 65%) or an incomplete partition typical of the classic Mondini deformity (4 ears, 20%). In the 4 nonsyndromic cases, one subject had bilateral Mondini dysplasia and the other three had normal cochleae. In the entire group, abnormalities of oval window development were common (20 of 30 ears, 67%), especially in the syndromic cases (18/22, 81%), but the round window was normal in the majority of cases (73%). Seven patients in the CHARGE association group had an anomalous course of the facial nerve, which was particularly severe in three. Four patients had congenital unilateral facial paralysis, although two of these children had normal radiographic anatomy of the facial nerve. One patient had bilateral facial weakness.
Conclusions: Syndromic and nonsyndromic cases of isolated semicircular canal aplasia were identified. Except for mild to moderate cochlear dysplasia, and the anomalous course of the facial nerve in some CHARGE association patients, both groups of patients were generally suitable for cochlear implantation if indicated. A high incidence of oval window aplasia with normal round window development may help to explain the embryopathogenesis of this anomaly, considering the sequence of inner ear development.