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

Background and purpose: Enhancement of the facial nerve can be seen on magnetic resonance imaging (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 post-contrast T-weighted, fat-saturated VIBE (volumetric interpolated breath-hold examination) sequence on both 1.5T and 3T scanners.

Materials and methods: Fifty patients without facial nerve symptoms undergoing MRI using the internal auditory canal (IAC) 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 two neuroradiologists.

Results: On 1.5T, out 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, out 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.

Abbreviations: IAC, Internal auditory canal; VIBE, Volumetric interpolated breath-hold examination.