Normal Facial Nerve Enhancement on Volumetric Interpolated Breath-Hold Examination MRI Sequence.

Abstract

Background and purpose: Enhancement of the facial nerve can be seen on MRI due to its rich arteriovenous plexus. Classically, enhancement of the facial nerve beyond the geniculate ganglion has been described as a normal finding, while enhancement of the canalicular and labyrinthine segments is considered abnormal. We hypothesize facial nerve enhancement of the canalicular and labyrinthine segments is a normal finding on the postcontrast T1-weighted, fat-saturated volumetric interpolated breath-hold examination (VIBE) sequence on both 1.5T and 3T MRI scanners.

Materials and methods: Fifty patients without facial nerve symptoms undergoing MRI by using the internal auditory canal protocol were identified at our institution, 25 cases on a 1.5T scanner and 25 cases on a 3T scanner; a total of 100 facial nerves. Presence or absence of enhancement of the facial nerve segments on the postcontrast T1-weighted, fat-saturated VIBE sequence were independently analyzed by 2 neuroradiologists.

Results: On 1.5T, of 50 facial nerves evaluated, percentage of nerves with enhancement at each segment was as follows: 80% canalicular, 92% labyrinthine, 100% tympanic, 100% mastoid, and 80% intraparotid. On 3T, of 50 facial nerves evaluated, percentage of nerves with enhancement at each segment was as follows: 60% canalicular, 84% labyrinthine, 98% tympanic, 100% mastoid, and 93% intraparotid.

Conclusions: Enhancement of the canalicular and labyrinthine segments of the facial nerve is a normal finding on the postcontrast, T1-weighted, fat-saturated VIBE sequence. Careful attention to clinical history and asymmetry should be considered before calling abnormality of the facial nerve.