Bilateral Symmetry and Variation of Recurrent Laryngeal Nerve and Inferior Thyroid Artery Patterns: An Intraoperative Study of 150 Nerves

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Abstract
The anatomical relationship of the inferior thyroid artery (ITA) and the recurrent laryngeal nerve (RLN) is highly variable. This study aims to evaluate bilateral RLN branching patterns and their relationship to the ITA within the same patient, predicting contralateral anatomical variations and ultimately reducing intraoperative risk of RLN injury. A retrospective review of prospectively collected intraoperative data was performed on adults undergoing total or completion thyroidectomy at a tertiary center between February 2022 and June 2025, with standardized documentation and intermittent nerve monitoring in all cases. RLN–ITA relation was classified as posterior, anterior, or between branches, and RLN morphology as single, bifurcated, or plexiform. Bilateral agreement, conditional probabilities, and predictors were evaluated using Cohen's κ and McNemar's test. Seventy‐five patients (150 RLNs) were included. Overall RLN–ITA relations were posterior 72.7%, anterior 24.7%, and between branches 2.7%. Extra‐laryngeal branching was observed in 24.7% of nerves (18% bifurcated, 6.7% plexiform). High bilateral agreement was demonstrated (κ = 0.83, p < 0.001), with 93.3% concordance between sides. When variation was present on one side, the probability of contralateral variation was 94.7% (left) and 81.8% (right). Variant RLN‐ITA relations were associated with larger median lobe volumes (21.7 vs. 12.3 mL), thought this trend did not reach statistical significance. Our study reveals a high degree of intra‐patient symmetry in both recurrent laryngeal nerve (RLN) branching patterns and the RLN‐ITA relationship, highlighting that anatomical variations are often mirrored contralaterally. While further larger‐scale studies are necessary to confirm the reproducibility of these findings, the identification of an RLN variation on one side should prompt greater caution during contralateral dissection.

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