CONTRAST ENHANCEMENT OF THE FACIAL-NERVE ON MRI - NORMAL OR PATHOLOGICAL

We prospectively analysed the normal contrast-enhanced MRI features of the facial nerve and determined criteria for pathological contrast en hancement. We studied 31 patients with clinically normal facial nerves with T1-weighted images before and after contrast medium. The intensi ty, thickness and right-left symmetry of enhancement were assessed in each segment and correlated with MRI features observed in abnormal fac ial nerves. Enhancement along at least one segment of the facial nerve was seen in 98 % of cases, but only within the facial canal: labyrint hine segment: 78.2 %; geniculate ganglion: 96.9 %; tympanic: 88.4 %; m astoid: 66.6 %. Marked (++) to intense (+++) enhancement was seen in t he labyrinthine segment in 17.4 %, the geniculate ganglion in 36.3 %, and the tympanic (25.6 %) and mastoid (7.1 %) segments, whereas intens e enhancement was only seen in the geniculate ganglion (6 %) and the t ympanic segment (11.6 %). A right-left asymmetry was noted in 69 % of cases. No correlation was found between enhancement and the thickness of the nerve. No enhancement of the eighth nerve was seen. We suggest three criteria for pathological enhancement: enhancement outside the f acial canal; extension of enhancement to the eighth nerve; and intense enhancement in the labyrinthine and/or mastoid segments.