Radiological evaluation of facial nerve and facial canal in patients with Bell's palsy.

Abstract

Purpose: To evaluate the diameter of the facial nerve (FN) and facial canal (FC) at different segments in Bell's palsy (BP) patients and compare the facial nerve/facial canal width ratio (FN/FC) of the the affected and healthy sides to determine the entrapped sites.

Methods: This retrospective study enrolled 47 patients with BP that were referred to a tertiary referral hospital. From patients' records, initial House-Brackmann grades, cranial computurized tomography (CT) and contrast enhanced temporal magnetic resonance imaging (MRI) scans were revieved. FC and FN diameter measurements were performed at the midpoint of labyrinthine segment, geniculate ganglion and tympanic segment in the axial plane, and mastoid segment in the sagittal plane. Contrast-enhanced segments on MRI were evaluated.

Results: There was no statistically significant difference between the FC diameters of the affected and the healthy sides on CT at any measured segments. FN diameter was increased significantly for all segments except mastoid segment on the affected side compared to the healthy side. FN/FC ratio was significantly greater on the affected side than the healthy side in all measured segments. Evident contrast enhancement was observed in all affected FNs, with geniculate ganglion and labyrinthine segment being the most common sites with contrast enhancement on MRI.

Conclusion: Anatomical differences in FC may not be the main predisposing factor in BP. As the geniculate ganglion and labyrinthine segments had the highest FN/FC ratio and showed clear contrast enhancement on MRI, these findings may indicate a higher risk of inflammation and entrapment in these segments.