Enhancement pattern of the normal facial nerve at 3.0 T temporal MRI

Abstract

The purpose of this study was to evaluate the enhancement pattern of the normal facial nerve at 3.0 T temporal MRI. We reviewed the medical records of 20 patients and evaluated 40 clinically normal facial nerves demonstrated by 3.0 T temporal MRI. The grade of enhancement of the facial nerve was visually scaled from 0 to 3. The patients comprised 11 men and 9 women, and the mean age was 39.7 years. The reasons for the MRI were sudden hearing loss (11 patients), Méniàre's disease (6) and tinnitus (7). Temporal MR scans were obtained by fluid-attenuated inversion-recovery (FLAIR) and diffusion-weighted imaging of the brain; three-dimensional (3D) fast imaging employing steady-state acquisition (FIESTA) images of the temporal bone with a 0.77 mm thickness, and pre-contrast and contrast-enhanced 3D spoiled gradient record acquisition in the steady state (SPGR) of the temporal bone with a 1 mm thickness, were obtained with 3.0 T MR scanning. 40 nerves (100%) were visibly enhanced along at least one segment of the facial nerve. The enhanced segments included the geniculate ganglion (77.5%), tympanic segment (37.5%) and mastoid segment (100%). Even the facial nerve in the internal auditory canal (15%) and labyrinthine segments (5%) showed mild enhancement. The use of high-resolution, high signal-to-noise ratio (with 3 T MRI), thin-section contrast-enhanced 3D SPGR sequences showed enhancement of the normal facial nerve along the whole course of the nerve; however, only mild enhancement was observed in areas associated with acute neuritis, namely the canalicular and labyrinthine segment.

Figure 1

A 46-year-old man with Méniàre's disease and normal facial nerves. (a) Post-contrast axial three-dimensional spoiled gradient record acquisition in the steady state MR scan demonstrates intense enhancement of the geniculate ganglion bilaterally (arrows) (Grade 3). (b) Right proximal tympanic segment (arrow) (Grade 1). (c) Axial scan of the left mastoid segment (arrow) shows a high-signal spot as intense as a visualised vessel (Grade 3). (d) Left parasagittal scan — the mastoid segment (arrows) is intensely enhanced and better visualised than in the axial scan.

Figure 2

Graph illustrating the enhancement pattern of the normal facial nerve from the canalicular to mastoid segment. GG, geniculate ganglion.

Figure 3

A 32-year-old man with right facial palsy: MR scan 7 days after onset of symptoms. (a) Pre-contrast axial T₁ fluid-attenuated inversion-recovery axial image of the facial nerve (arrows) at the cerebellopontine angle (CP) angle. (b) Contrast-enhanced three-dimensional spoiled gradient record acquisition in the steady state scan shows intense enhancement of the distal meatal and labyrinthine segments of the right facial nerve (arrows) (Grade 3).