Cross-sectional anatomy of the facial nerve.

The length and complexity of the anatomical course of the facial nerve explains the difficulty of its accurate morphologic evaluation. CT and MR appear to be complementary techniques to precisely depict the nerve from its pontine origin to the parotid gland. Anatomical variations exist in length or thickness of all intrapetrous segments or as frequent dehiscences which can lead to false positive results or at the opposite falsely negative diagnoses. Close relations with the antero-inferior cerebellar artery in the intracisternal and intracanalicular segments must be known. Gadolinium enhancement is usual in the fallopian canal with variable intensity and thickness and should be differentiated from pathological enhancement. Finally the intrapetrous course of the chorda tympani can be precisely displayed on CT in the intra-osseous canal and in the middle ear near the ossicles.