Radiologic evidence for absence of the facial nerve in Mobius syndrome.

OBJECTIVE: To detail the radiologic findings in Mobius syndrome, in order to clarify its pathogenetic mechanisms. METHODS: High resolution three-dimensional T1 (MP rage) and T2 (CISS) weighted MRI were used to study the cisternal and canalicular portion of the seventh cranial nerve in six Mobius patients. Also, the anteroposterior dimension of the brainstem was measured at the level of the pons in the authors' 6 patients and in 20 age-matched healthy control subjects. Furthermore, the MRIs were evaluated for associated congenital brain anomalies. RESULTS: The facial nerves were absent in all six patients despite residual function in some facial muscles. The authors confirmed brainstem hypoplasia but did not find tegmental calcifications. The anteroposterior dimension of the brainstem ranged between 17 and 25 mm vs 20 to 27 mm for controls. In three patients there were congenital abnormalities in the posterior fossa. CONCLUSION: The absent facial nerves on MRI and the unusual distribution of the facial weakness, which is characteristic of Mobius syndrome, suggests that other cranial nerves, possibly the trigeminal, hypoglossal, or glossopharyngeal nerve, aberrantly innervate some lower facial muscles. Radiologic findings support the notion that Mobius syndrome is part of a more complex congenital anomaly of the fossa posterior