[A case of atypical hemifacial spasm without involvement of orbicularis oculi muscles: possibility of functional topography in facial nerve].

We reported a case of atypical hemifacial spasm that did not involve orbicularis oculi muscles. A 60-year-old woman suffered from intermittent involuntary movement of the orbicularis oris and buccinator muscles. Operative findings revealed that the rostrodorsal portion of the facial nerve root was compressed by a loop of AICA. Transposing this AICA, it was found that it was compressing one portion on the rostrodorsal part of this nerve root. In most cases, facial spasm involves orbicularis oculi muscles and compression of the anatomically caudal portion of the facial nerve root. Differentiation of the compressed portions of the nerve, therefore, may indicate a functional topography of the facial nerve.