Significance of facial canal labyrinthine segment diameter in the pathophysiology of Bell′s palsy

Abstract

Aims and Objectives: To analyze whether there is a significant difference in the width of the labyrinthine segment of the facial canal between the affected and the unaffected sides in cases of unilateral Bell's palsy, and also to ascertain whether there is any correlation between the degree of facial nerve degeneration and the width of the facial canal.Study Design: Prospective observational study. Setting: Tertiary care university hospital. Material and Methods: A total of 30 patients with unilateral Bell's palsy underwent high-resolution computed tomography with 1-mm-thick contiguous axial sections. The width of the labyrinthine portion of the facial canal at its proximal end (meatal foramen) and at the mid-labyrinthine portion was assessed on both the affected and the unaffected sides and was compared using the paired t tests. Nerve conduction studies were done to assess the degree of facial nerve degeneration. The percentage of facial nerve degeneration was compared with the width of the labyrinthine portion of the facial canal at both the aforementioned sites using the t tests of significance. Results: The width of the labyrinthine segment, both at the meatal foramen and at the mid-labyrinthine part, was significantly different on the affected side as compared with the unaffected side. The degree of facial degeneration was assessed using nerve conduction studies. Majority of the patients with less than 50% degeneration recovered within 1 month, and by 2 months, 100% of patients recovered, including those with more than 75% degeneration. The compound action potentials did not correlate significantly with the width of the facial canal. Conclusion: The width of the labyrinthine segment of the facial canal may be a potential predisposing factor in the etiopathogenesis of Bell's palsy. The degree of facial nerve degeneration, however, did not correlate with the narrowing of the labyrinthine segment of the facial canal on the affected side in Bell's palsy.