CT and MR findings of Michel anomaly: inner ear aplasia.

In 1863, Michel described a condition characterized by a total absence of differentiated inner ear structures associated with other skull base anomalies, including an abnormal course of the facial nerve and jugular veins. Michel aplasia clearly differs from Michel dysplasia, in which arrest of embryologic development occurs later. Recently, the role of otic capsule formation on mesenchymal differentiation was reported as well as the impact of the genetic deletion of the homeobox gene on the development of the ear, cranial nerves, and hindbrain. We report two patients with a total absence of inner ear structures bilaterally, illustrating the characteristic appearance of Michel aplasia and associated skull base anomalies.