Essays on the facial nerve: Part I. Microanatomy

Facial nerve explorations and microstimulation of distal nerve branches during facial reanimation procedures by the senior author (J.K.T.) have yielded various observations. This prompted the authors to quantify the surgical findings with an anatomical study and a subsequent analysis of the electrophysiologic intraoperative data. The present report details the microanatomical observations.

Ten fresh cadaveric hemiface dissections (five specimens) were performed. The facial nerve branches were traced distally under the operating microscope and mapped with India ink. A number of nerve branches exited the parotid at approximately 9 +/- 0.85 cm from the facial nerve trunk division, and their distribution was noted. Photographic documentation was obtained.

The mean number of nerve branches was 7.70 +/- 1.05 at the anterior parotid border and 13.80 +/- 1.81 distally. Differences in the number and configuration of nerve branches existed even between the two sides of the face. The frontal branch had a mean nerve number of 2.80 +/- 0.63; the zygomatic branch, 4.40 +/- 1.34, the buccal branch, 3.20 +/- 0.78; and the marginal mandibular branch, 2.30 +/- 0.48. In 70 percent of specimens, the buccal branches originated from both upper and lower nerve divisions and interconnected with the marginal mandibular branch in 50 percent of specimens. Distally, connectivity was found between buccal branches and the infraorbital nerve, the marginal mandibular branches, and the mental nerve. A constant lower zygomatic or zygomaticobuccal branch reached the procerus and corrugator supercilii muscles. A twig from the frontal branch reached the corrugator muscle in 60 percent of cases.

Diversity of facial nerve anatomy is recognized and documented. Specific anatomical relationships are clarified and demonstrated as a guiding map.