Enhancement along the normal facial nerve in the facial canal: MR imaging and anatomic correlation

Normal facial nerves are reported to show no enhancement at magnetic resonance (MR) imaging, in contradiction to the authors' clinical experience. To investigate this inconsistency, the authors searched MR imaging files and clinical records to find patients who underwent MR imaging of the temporal bone (at 1.5 T) before and after intravenous administration of gadopentetate dimeglumine and who had bilateral clinically normal facial nerves. When the MR images of 93 patients (186 facial nerves) were analyzed subjectively, 142 nerves (76%) were visibly enhanced along at least one segment of the facial nerve within the facial canal; the nerves of 64 of the 93 patients (69%) showed right-left asymmetry in enhancement, which was inhomogeneously distributed along each nerve. The facial nerve in the cerebellopontine angle cistern and in the internal auditory canal, as well as in the visualized proximal portion of the extracranial facial nerve, showed no enhancement. Comparison with reference anatomic sections showed that this enhancement pattern corresponded exactly to the topography of the circumneural facial arteriovenous plexus and should not necessarily be considered a sign of anatomic abnormality.