Austin Hembd

Facial Nerve Axonal Analysis and Anatomical Localization in Donor Nerve: Optimizing Axonal Load for Cross-Facial Nerve Grafting in Facial Reanimation.

Background: Donor nerve axonal count over 900 in two-stage reconstructions using cross-facial nerve grafts is possibly associated with improved outcomes in facial reanimation. Facial nerve axonal analysis was performed to determine the ideal location for optimizing axonal load. Correlation of axonal number, branch diameter, and age was also assessed. Methods: Twenty-eight fresh unpreserved cadaveric hemifaces were dissected exposing the extracranial facial nerve branches. Axonal counts at 2-cm intervals from the pes anserinus along branches inserting into the zygomaticus major muscle were taken, noting position relative to the zygomatic arch, posterior ramus border, lateral border of the zygomaticus muscle, and anterior parotid gland border. Nerves were fixed, sectioned, and stained with SMI-31 antineurofilament stain for digital axonal analysis. Results: All specimens had one or more intraparotid zygomatic branches with over 900 axons, and 96 percent 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, 6 mm posterior to the parotid border) was 92 percent (range, 67 to 100 percent) in contrast to 61 percent (range, 25 to 100 percent) when sampled at the first extraparotid point (mean, 14 mm anterior to the parotid border). Nerve cross-sectional area was positively correlated to its axonal count (R° = 78 percent; p < 0.0001), with nerve diameter over 0.6 mm predicting over 900 axons. Age did not correlate with axonal counts. Conclusions: Branches with adequate axonal load were found in all specimens. The likelihood of adequate branch selection improved from 61 percent to 92 percent with short retrograde intraparotid dissection. Nerve diameter correlated with axonal load.

Correlation Between Facial Nerve Axonal Load and Age and Its Relevance to Facial Reanimation

Background: Two-stage facial reanimation procedures with a cross-facial nerve graft often have unsatisfactory results in the older patient. Although the cause of result variability is likely multifactorial, some studies suggest that increased donor nerve axonal load improves function of a free muscle transfer after a cross-facial nerve graft. This study attempts to characterize the relationship between age and facial nerve axonal load. Methods: Sixty-three fresh cadaveric heads were dissected to expose the facial nerve. For each hemiface, two facial nerve samples were taken: one proximal as the nerve exits the stylomastoid foramen, and one distal at the buccal branch (at a point 1 cm proximal to the anterior parotid border). Nerve samples were stained and quantified. Correlation analysis was completed using a Pearson correlation coefficient. Results: Thirty-six female and 27 male cadavers were dissected; their average age was 71 years (range, 22 to 97 years). At the proximal (r = −0.26; p < 0.01; n = 104) and distal (r = −0.45; p < 0.0001; n = 114) sampling points, there was a significant negative correlation between age and axonal load. Conclusions: As age increases, the axonal load of the facial nerve decreases at the buccal and zygomatic branches approximately 1 cm proximal to the anterior parotid border. The authors previously suggested this location as significant for cross-facial nerve coaptation. These results propose that decreasing axonal load can be a factor in the unsatisfactory outcomes of cross-facial grafting in the aging population. Moreover, this underscores the importance of recruiting more donor axons in attempting to improve facial reanimation in the older patient.

The Deep Temporal Nerve Transfer: An Anatomical Feasibility Study and Implications for Upper Facial Reanimation.

Background: Facial paralysis has a profound impact on the brow, and currently static procedures are the mainstay of treatment. The deep temporal branches of the trigeminal nerve, given their proximity to the brow, may serve as possible donor nerves for both potential innervation of a free muscle transfer in patients with prolonged facial palsy or nerve transfers in acute or subacute palsy. As such, the authors present the detailed surgical anatomy of the deep temporal nerve, assessing feasibility for both functional muscle and nerve transfers, including a proposed surgical technique. Methods: Thirty cadaver hemifaces were dissected to establish deep temporal nerve anatomy and perform axonal analysis. Results: Two (53 percent) or three (47 percent) divisions of the deep temporal nerve were noted, with the most consistent division being the middle division (30 of 30 specimens). This division was consistently found approximately 4.1 cm (range, 3.7 to 4.5 cm) anterior to the tragus at the level of the zygomatic arch. For each 1 cm cranial to the arch, the nerve courses approximately 1 mm posteriorly. The number of axons in the proposed temporal branch is 1469 as it emerges from behind the zygomatic arch, 889 at 1 cm, 682 at 2 cm, 534 at 3 cm, 355 at 4 cm, 377 at 5 cm, and 256 at 6 cm. Conclusion: Given its anatomical consistency, and expendability, the middle division of the deep temporal nerve is a viable donor nerve for dynamic upper facial reanimation with either nerve transfer or functional muscle transfer, depending on the length of facial palsy. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V.