(412) Quantitative Model of Decompression Surgery for Bell’s Palsy

Introduction: Decompression surgery has been advocated to reduce risk of permanent facial synkinesis and disfigurement in a subset of Bell’s Palsy patients, but its study has been limited and to date no animal model exists to simulate this procedure. Described is the design and validation of an implantable device for inducing unilateral facial nerve compressive neuropathy in a rat model and correlating with long-term functional recovery.

Methods: An implantable device was designed to allow precise titration and real-time measurement of pressure in a vascular occlusion cuff. Three Lewis rats were then implanted with these devices and vascular occlusion cuffs placed around branches of the facial nerve controlling whisker movements on one side. Cuffs were inflated to low-pressure (0-100mmHg), medium-pressure (200-300mmHg), or high-pressure (300-500mmHg) ranges for 5 days. Whisking activity was quantified daily to assess nerve function. Cuffs were then deflated and explanted, and whisking activity measured 10 weeks. Histological analysis of axon count and diameter using FluorMyelin GreenTM staining was performed.

Results: Low-pressure neural compression demonstrated no functional loss and no change in mean axon count or diameter consistent with uninjured nerve. Medium-pressure compression demonstrated partial functional loss and full recovery within one day of decompression, with moderately increased axon count and decreased axon diameter consistent with Sunderland grade III injury. High-pressure compression demonstrated full functional loss without recovery within 10 weeks, with pronounced thinning on gross examination and markedly-increased axon count and decreased axon diameter consistent with Sunderland grade V injury.

Conclusions: This is the first characterization of the relationship between neural compression and long-term recovery of facial function a live animal model. This model may be used to evaluate 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.