Complete labyrinthine aplasia: clinical and radiologic findings with review of the literature.

BACKGROUND AND PURPOSE Complete labyrinthine aplasia (CLA), also referred to as Michel aplasia, is a severe congenital anomaly of the inner ear, defined by the complete absence of inner ear structures. The purpose of this study was to document the imaging findings in a series of patients with CLA, with review of the literature, to better understand this anomaly. MATERIALS AND METHODS The CT and MR imaging findings of 9 patients (14 ears with CLA) were retrospectively evaluated. The audiologic tests and patient charts were also retrospectively reviewed. RESULTS CLA was bilateral in 5 and unilateral in 4 patients. The petrous bone was hypoplastic in all 14 ears, but the otic capsule was aplastic in only 5. The middle ear and mastoid volumes were decreased in most of the ears. The stapes was aplastic in 1 ear and was dysplastic in 5 ears. The internal acoustic canal was aplastic in 4 ears and markedly narrowed in 10 ears. The facial nerve canal showed a variety of anomalies and aberrant courses in 11/14 ears. The bony covering of the jugular bulb was defective in 9 ears. Tegmen tympani defects were seen in 3 patients, and there were several accompanying skull base and posterior fossa anomalies. CONCLUSIONS Although CLA is a rare developmental anomaly, its accurate diagnosis and its differential diagnosis from labyrinthine ossificans is crucial. Proper guidance of these patients for brain stem implantation in the critical period of brain development depends on the recognition of the characteristic imaging findings of CLA.