Anatomy of the facial nerve (spatial orientation of fibers in the temporal bone).

Abstract

AbstractThe spatial relations of the peripheral branches of the facial nerve within the temporal bone were studied. Five groups of experiments were performed, using 48 adult cats. The topographical anatomy of the horizontal segment was demonstrated by evoked EMG in two cats with injuries to the lateral aspect of the horizontal segment of the facial nerve. The upper face was more severely injured than the lower. The cross sectional spatial anatomy of the horizontal segment of the facial nerve was mapped out in seven cats by histopathologically correlating the lesion site with the peripheral distribution. Gross dissections in 14 cats demonstrated the cross sectional spatial relationships of the peripheral fibers at the stylomastoid foramen and distal portion of the vertical segment. Temporal bone sections in five cats added further to the orientation of the facial nerve.The following conclusions were drawn from this study: The facial nerve was spatially oriented in its tympanomastoid segment; the branches to the ear and chorda tympani nerve were lateral (toward the mastoid cortex); the forehead and eye lateroanterior (toward the middle ear); the lower lip anteromedial (toward the floor of the middle ear); the upper midface posterior (toward the horizontal canal), and the lower midface just anterior to the upper midface. The peripheral fibers rotated as they coursed from the stylomastoid foramen toward the face; the lower branches twisted under and medial to the branch just above them. The lower face branches twisted from an anteromedial position in the horizontal segment to a posteromedial position at the stylomastoid foramen. The upper midface branches changed position from a posterolateral position at the horizontal segment to anteromedial at the stylomastoid foramen. The branch to the stapedial muscle separated from the horizontal segment of the facial nerve from a posteromedial position. The branch to the stylohyoid muscle and posterior bolly of the digastric muscle separated from the facial nerve just beyond the stylomastoid foramen from a posteromedial position. A review of the literature suggested a close resemblance between the anatomy of the facial nerve in cat and man; therefore, the detailed anatomy of the cross section of the cat's facial nerve within the temporal bone should have direct clinical application.