Landmark-Based Localization of the Ansa Cervicalis and Recurrent Laryngeal Nerve for Anastomotic Reinnervation: A Cadaveric Study

Background/Objectives: Ansa-cervicalis-to-recurrent laryngeal nerve (ARA) anastomosis is an established reinnervation procedure for unilateral vocal fold paralysis (UVFP). Successful surgery requires reliable identification of the ansa cervicalis motor entry point and the recurrent laryngeal nerve (RLN) laryngeal entry point to facilitate tension-free anastomosis while avoiding neurovascular injury. Their positions relative to a single palpable external landmark have not been quantified. Methods: Thirty-two ansa cervicales and corresponding RLNs were dissected from 23 formalin-embalmed cadavers. Mediolateral and superoinferior distances from each nerve entry point to the inferior border of the thyroid cartilage at the midline laryngeal prominence were measured and combined into a Euclidean landmark-referenced straight-line distance. Ansa cervicalis root lengths and branching patterns were also documented. Results: The mean straight-line distance was 43.3 mm (SD 9.7) for the ansa cervicalis and 55.5 mm (SD 11.7) for the RLN laryngeal entry point. The paired analysis mean difference in landmark-referenced straight-line distance was 12.2 mm (95% CI 8.3–16.0; p < 0.001), driven primarily by a mediolateral difference of 13.6 mm (p < 0.001). Mean lengths were 34.7 mm for the superior root, 38.6 mm for the inferior root, and 42.6 mm for main branch. No statistically significant differences were detected by sex or laterality. A three-root variant was observed in 6.25% of cases. Conclusions: The RLN laryngeal entry point is about 12 mm farther from the shared landmark than the ansa cervicalis motor entry point, with the difference primarily attributable to mediolateral position. This relationship may warrant intraoperative evaluation as a supplemental spatial reference during ARA dissection.