A Quantitative Model for Decompression Surgery in Bell's Palsy

Abstract

Bell’s palsy is an idiopathic mononeuritis of the facial nerve thought to result from viral reactivation, causing inflammation and subsequent compression of the nerve within the rigid confines of the temporal bone. While most affected patients eventually recover normal facial function, aberrant neural regeneration occurs in a subset of Bell’s patients who present with severe facial weakness at onset, resulting in permanent facial synkinesis and disfigurement. Neural decompression surgery to alleviate pressure on the facial nerve in the acute setting of severe Bell’s palsy has been advocated as means to reduce risk of development of long-term sequelae, but use of this procedure has been limited and its efficacy is not well understood. Described is the design and validation of a rat model for unilateral compressive neuropathy of the facial nerve with the ability to examine long-term functional recovery associated with various durations and degrees of neural compression. Animals were implanted with vascular occlusion cuffs around branches of the facial nerve controlling whisker movements on one side, and cuffs inflated to various pre-set pressures for five to seven days. Whisking activity was quantified daily to characterize the threshold extrinsic pressure required to induce palsy. Cuffs were then be deflated and explanted, and whisking activity tracked and compared between sides over the ensuing 10 weeks. Functional nerve recovery and histological analysis of compressed nerves were then evaluated to determine the pressure range in which a Bell’s-like phenomenon is observed in this rat model. This work is the first to characterize the relationship between neural compression pressure and long-term recovery of facial function in highly quantitative and controlled fashion in a live animal model. Future work will seek to characterize the relationship between the timing of neural decompression and long-term facial function, providing evidence to support or refute the utility of mechanical decompression of the facial nerve in the setting of acute Bell’s palsy.