IDIOPATHIC, HERPETIC, AND HIV-ASSOCIATED FACIAL-NERVE PALSIES - ABNORMAL MR ENHANCEMENT PATTERNS

PURPOSE: To determine specific criteria that can be used to define nor mal versus abnormal MR contrast enhancement of the facial nerve. METHO DS: Twenty-three patients with acute unilateral inflammatory periphera l facial nerve palsy were examined on a 1.5-T MR using multiplanar T1- weighted spin-echo sequences before and after injection of gadopenteta te dimeglumine. These MR patterns were compared with those of healthy control subjects. RESULTS: The normal facial nerve usually showed a mi ld to moderate enhancement of the geniculate ganglion and the tympanic -mastoid segment. The intracanalicular-labyrinthine segment did not en hance. All patients showed abnormal enhancement of the distal intracan alicular and the labyrinthine segment. An intense enhancement could be observed in the geniculate ganglion and the proximal tympanic segment , especially in herpetic palsy. Associated enhancement of the vestibul ocochlear nerve was seen in herpetic and idiopathic palsy. Enhancement of the inner ear structures was detected only in herpetic palsy. CONC LUSIONS: Abnormal contrast enhancement of the distal intracanalicular and the labyrinthine facial nerve segment is observed in all patients and is the only diagnostically reliable MR feature proving an inflamma tory facial nerve lesion. The intense enhancement of the geniculate ga nglion and the proximal tympanic segment is possibly correlated with t he reactivation of the latent infection in the sensory ganglion. The a bnormal enhancement results from breakdown of the blood-peripheral ner ve barrier and/or from venous congestion in the venous plexuses of the epi- and perineurium.