Organization and Microscopic Anatomy of the Adult Human Facial Nerve: Anatomical and Histological Basis for Surgery

Abstract

Despite the progress in microsurgical repair of the facial nerve, the results remain unpredictable and the structural anatomy of the facial nerve poorly understood. The aim of this study was to show how the connective tissue and the nerve fibers are distributed in a serial cross-section of the facial nerve from its origin to its termination. Sixty facial nerves from 30 embalmed adult human cadavers were dissected for micro-anatomic study. The facial nerves were serially sectioned every 2 mm from the apparent origin and were prepared for light microscopy study. The endoneural fascicular arrangement was observed, the number of myelinated fibers was counted, and connective tissue was explored. There was an absence of real fascicular organization of the facial nerve in the pontocerebellar cistern and in the internal acoustic meatus. The real fascicular organization with perineurium and epineurium appeared from the geniculate ganglion. The number of fascicles increased in a proximo-distal way, and their diameter diminished. In the extratemporal part, some nerves had a low number of fascicles (two to six), and others had a high number of fascicles (seven to 15). The number of fascicles changed along the course of the facial nerve, especially in the extratemporal part. The truly fascicular structure appeared after the geniculate ganglion, and the rate of connective tissue progressed in a proximo-distal way. The high numbers of fascicles and the great structural variability of each facial nerve segment constitute a difficulty in nerve repair.