A rare case of aberrant facial nerve course in the mastoid segment

Abstract

Facial nerve is the main motor supply to the part of facial skeleton system responsible for expressions. The reported rate of iatrogenic injury to the facial nerve in primary mastoid surgeries was 0.6% to 3.7%. Temporal bone is one of the most complex anatomical parts of human body. A variety of facial nerve courses has been described in literature. Normally, horizontal segment of the facial nerve traverses from geniculate ganglion to second genu which is usually situated medial and inferior to lateral semicircular canal. From here it passes posteriorly and laterally along the medial wall of the middle ear. Mastoid or vertical segment extends from the second genu to stylomastoid foramen deep to tympano-mastoid suture line from where the nerve exits out of the temporal bone. During our endoscopic dissection we encountered a grossly anomalous course of facial nerve in which after turning at second genu, the nerve curves posteriorly and lies in the floor of mastoid cavity and traverse’s its whole length of mastoid and instead of moving out of foramen it travels towards sinus plate and then takes another (3rd) turn to travel anteriorly towards the tip of mastoid from where it finally exits.