Correlation Between Facial Nerve Axonal Load and Age and its Relevance to Facial Reanimation
Austin Hembd, M.D.1, Purushottam Nagarkar, M.D.1, Justin Perez, M.D.1, Andrew Gassman, M.D.1, Philip Tolley, B.S.1, Joan Reisch, Ph.D.2, Charles L. White, III, M.D.3, Shai M. Rozen, M.D.1.
1Department of Plastic Surgery; University of Texas Southwestern Medical Center, Dallas, TX, USA, 2Division of Biostatistics; University of Texas Southwestern Medical Center, Dallas, TX, USA, 3Department of Pathology, Division of Neuropathology; University of Texas Southwestern Medical Center, Dallas, TX, USA.
Purpose: Two-stage facial reanimation procedures with a cross-facial nerve graft often yield less predictable results in older patients due to multifactorial reasons. Some studies strongly suggest that increased donor nerve axonal load improves function of a free muscle transfer after a cross-facial nerve graft. However, strong studies characterizing the relationship between age and facial nerve axonal counts do not exist, possibly providing an explanation for the variable results as we age.
Methods: In the largest study of its kind, 63 fresh, cadaveric heads were dissected to expose the facial nerve. For each hemi-face, two facial nerve samples were taken: one proximal as the nerve exits the stylomastoid foramen, and one buccal branch sample at a point 1-cm proximal to the anterior parotid border, a donor location previously described as having appropriate donor axonal load. 252 nerve samples were stained and quantified. Correlation analysis was completed using a Pearson's correlation coefficient.
Results: 36 females and 27 males were dissected with an average age of 71 (age range 22-97). At the proximal (r =-.26;p<.01;n=104) and distal (r= -.45;p <.0001;n=114) sampling points, there was a significant negative correlation between age and axonal load.
Conclusion: As age increases the axonal load of the facial nerve decreases. These results indicate that decreasing axonal load could be a contributing factor in the variable outcomes of cross-facial grafting in the elderly. Moreover, this underscores the importance of recruiting more donor axons in attempting to improve facial reanimation in the older patient.
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