Facial nerve MRI enhancement in various pathological entities

ABSTRACT

The facial nerve serves motor, sensory and autonomic functions. Anatomical variations exist in length or thickness of all intra-petrous segments as frequent dehiscence that can lead to false diagnosis. Enhancement of facial nerve could be noted in normal and abnormal cases, the familiarity of radiologists for normal enhancement of different parts of the nerve can help to detect pathological conditions as Bell's palsy, tumors and other diseases. The aim of the study was to demonstrate the difference in enhancement patterns of facial nerve segments in normal individuals and various pathological conditions. The MRI findings of 156 patients were evaluated. All patients were examined on the 1.5 Tesla MR Unit using head coil. Contrast material was injected intravenously using a bolus of 0.1 mmol/kg body weight. The evaluation of contrast enhancement was mainly based on visual inspection and comparison between pre- and post-contrast images at the same planes. The facial nerve segment was considered enhancing when there were increased signals of that segment compared to the pre-contrast images. The intensity, thickness and right-left symmetry of enhancement were assessed in each segment. The studied cases were divided into seven groups including normal cases in seventy-eight, acute Bell's palsy in twenty six cases, Necrotizing External Otitis in nine cases, Congenital disorders in eight cases, Tumors in nineteen cases and Petrous apicitis, Cholesteatoma, Chronic Otitis Media in fourteen cases and multiple sclerosis in two cases. This study concluded that the transverse tympanic and proximal vertical mastoid segment may enhance in normal population, due to the presence of a rich perineural venous plexus surrounding the nerve in the fallopian canal. The study suggests three criteria for pathological enhancement enhancement outside the facial canal; extension of enhancement to the eighth nerve; and intense enhancement in the labyrinthine and/or mastoid segments. We concluded that contrast enhancement of the distal intrameatal and a labyrinthine segment is specific for facial nerve palsy. The disappearance of facial nerve enhancement was found to be related to improvement in facial nerve function during recovery from Bell's palsy. The intensity of contrast enhancement did not correspond to the severity or duration