Anomalous facial nerve canal with cochlear malformations

BACKGROUND AND PURPOSE: Anteromedial "migration" of the fil st segment of t he facial nerve canal has been previously identified in a patient with a no n-Mondini-type cochlear malformation. In this study, several patients with the same facial nerve canal anomaly were reviewed to assess for the associa tion and type of cochlear malformation. METHODS: CT scans of the temporal bone of 15 patients with anteromedial mig ration of the first segment of the facial nerve canal were collected from r outine departmental examinations, In seven patients, the anomalous course w as bilateral, for a total of 22 cases. The migration was graded relative to normal as either mild/moderate or pronounced, The cochlea in each of these cases was examined for the presence and size of the basilar, second, and a pical turns, The turns were either absent, small, normal, or enlarged, The CT scans of five patients with eight Mondini malformations were examined fo r comparison. RESULTS: The degree of the facial nerve migration was pronounced in nine ca ses and mild/ moderate in 13. All 22 of these cases had associated cochlear abnormalities of the non-Mondini variety, These included common cavity ano malies with lack of definition between the cochlea and vestibule (five case s), cochleae with enlarged basilar turns and absent second or third turns ( five cases), and cochleae with small or normal basilar turns with small or absent second or third turns (12 cases). None of the patients with Mondini- type cochlear malformations had anteromedial migration of the facial nerve canal. CONCLUSIONS: Anteromedial migration of the facial nerve canal occurs in ass ociation with some cochlear malformations, It did not occur in association with the Mondini malformations. A cochlea with a Mondini malformation, bein g similar in size to a normal cochlea, may physically prohibit such a devia tion in course.