Evaluation of Bell's palsy in the cerebellopontine angle: An MRI study.

Background: Evaluation of cranial nerve morphology through measuring cross-sectional area (CSA) on magnetic resonance imaging (MRI) is increasing day-by-day in clinical diseases. In Bell's palsy (BP), the manifestation of the enlarged CSA of the facial nerve (FN) may be used for diagnosis. This study aims to evaluate whether there is an enlargement of the cisternal FN in BP.

Methods: This retrospective study included 43 patients diagnosed with BP. In the reconstructed MRI, the long (LD) and short (SD) diameters of the paralytic and normal sides of the FNs located in the cerebellopontine angle were measured, and the CSA was calculated using the Radinsky formula. Before the radiologic measurement, a preliminary experiment was carried out on the rat sciatic nerve to be able to determine the actual nerve boundary on MRI.

Findings: There was a statistically significant relationship between paralytic and normal sides in the measurements of LD, SD, and CSA. The paralytic side was larger than the normal side in the cisternal FN. According to the Receiver Operating Characteristic (ROC) curve, BP can be estimated with 60% sensitivity and 70% specificity by the CSA of the FN more than 1.04 mm . As a result of the preliminary experiment, it was found that the actual nerve boundary was at approximately 50% intensity between the minimum and maximum values.

Conclusion: Although entrapment of FN in the labyrinthine segment in BP was known, this study showed that the cisternal FN, which could be evaluated more conveniently, enlarged in the paralytic side compared with the normal side, and revealed the necessity of performing the comparison amongst the MRI studies on BP patients by a standardised measurement method. This study will also help clinicians to make a decision in the diagnosis of BP by giving a cut-off value for the CSA.