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Facial Nerve Axonal Analysis and Anatomic Localization of Donor Nerve - Optimizing Axonal Load for Cross Facial Nerve Grafting in Facial Reanimation
Purushottam Nagarkar, MD1, Austin Hembd, BS1, Dinah Wan, MD1, Salim Saba, MD2, Walter Kutz, MD1, Brandon Isaacson, MD1, Sachin Gupta, MD1, Shai Rozen, MD1.
1University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA, 2American University of Beirut, Beirut, Lebanon.

PURPOSE:
Donor nerve axonal count over 900 is associated with improved outcomes in facial reanimation with free functional muscle. We measured axonal counts of facial nerve zygomatic branches at multiple points to determine the ideal location for optimizing axonal load.
METHODS:
28 fresh unpreserved cadaveric hemi-faces were dissected to expose the extracranial facial nerve branches. Zygomatic branches were harvested in 2 cm sections from the pes anserinus distally, noting their position relative to the zygomatic arch, posterior border of ramus, lateral border of zygomaticus major and anterior border of parotid gland. Nerves were fixed, sectioned, stained with SMI-31 anti-neurofilament stain, and digitally analyzed for axonal counts.
RESULTS:
The mean number of axons in the facial nerve at the pes anserinus was 4220. All specimens had one or more intraparotid zygomatic branches with over 900 axons, and 96% had an extraparotid branch with over 900 axons. The likelihood that a zygomatic branch would have over 900 axons at its last intraparotid point (mean 6mm posterior to parotid border) was 92%. By contrast, this likelihood was only 61% when sampled at the first extraparotid point (mean 14mm anterior to parotid border). The cross-sectional area of a branch was positively correlated to its axonal count (R² = 78%, p=<.0001), with nerve diameter over 0.6mm predicted to have over 900 axons.
CONCLUSION:
Branches with adequate axonal load were found in all specimens. The likelihood of selecting an adequate branch improved from 61% to 92% when dissected intraparotid. Nerve diameter positively correlated with axonal load.


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