The NRLN is an uncommon but clinically important anatomic variant in which the inferior laryngeal nerve fails to follow its usual recurrent course. Pooled data from a large meta-analysis estimate the prevalence of a right NRLN at approximately 0.7% of right-sided nerves at risk (95% CI 0.6–0.9%) [5], closely matching the 0.51% operative incidence (31 of 6,000 thyroidectomies) reported in one of the largest single-institution surgical series. [3] A left-sided NRLN is exceedingly rare and is essentially confined to patients with a right-sided aortic arch or situs inversus. Toniato et al. proposed an operative classification still widely used today: type 1, in which the nerve runs with the superior thyroid pedicle; type 2A, in which it crosses above or parallel to the inferior thyroid artery; and type 2B, in which it passes below the artery or between its branches [3]. The nerve in the present case corresponded to a type 2A configuration.

Embryologically, the right NRLN results from abnormal regression of the right fourth aortic arch and the proximal right dorsal aorta. The right subclavian artery consequently arises as the last (most distal) branch of the aortic arch — the arteria lusoria — and follows a retroesophageal course to reach the right upper limb. [6] Because the vessel that would normally tether the developing inferior laryngeal nerve caudally into the thorax is absent, the nerve is not drawn down into a recurrent loop and instead passes directly from the vagus to the larynx.

The association between ARSA and right NRLN is one of the most consistent anatomic–vascular correlations in endocrine surgery. In the meta-analysis by Henry et al., 86.7% of right NRLNs were associated with an aberrant subclavian artery. [5] In a focused review of 104 NRLN cases with documented vascular variants, 97.7% were right-sided, and ARSA was present in 97% of these. [7] The converse relationship is equally strong: in a controlled ultrasound study, an NRLN was identified only among patients in whom an ARSA had first been demonstrated, and never in matched controls without ARSA (p = 0.0006). [8] In practical terms, identification of an ARSA on any preoperative imaging should be treated as a near-certain predictor of a right NRLN.

This association underlines the value of preoperative cross-sectional imaging review. CT can demonstrate the retroesophageal course of the aberrant artery directly [9], and a dedicated neck ultrasound can suggest the diagnosis by the absence of the normal brachiocephalic (innominate) bifurcation in the supraclavicular fossa. [10-12] In the present case, a contrast-enhanced CT had already been obtained for an unrelated indication (dysphagia and compressive symptoms), and the ARSA was visible on both axial and sagittal sequences, yet it was only recognized on retrospective review after surgery. This represents a missed opportunity for preoperative anticipation and is, in our view, the most actionable teaching point of this report: surgeons should routinely and specifically screen any available preoperative neck or chest cross-sectional imaging for ARSA before right-sided thyroid or parathyroid dissection, regardless of the indication for which the scan was originally obtained.

Intraoperatively, careful visual dissection remains the gold standard for identifying the NRLN, but intraoperative neuromonitoring (IONM) using a vagus-first stimulation algorithm — stimulating the vagus nerve both proximally and distally in the neck before paratracheal dissection — can predict a non-recurrent course before the nerve is put at risk, and has been shown to increase intraoperative detection rates. [13-16] IONM was not used in the present case; identification relied on meticulous capsular dissection and proximal tracing of the nerve to its vagal origin within the carotid sheath. Although the outcome was favorable, we believe that in any patient with a known or suspected ARSA, a vagus-first IONM protocol, performed in line with International Neural Monitoring Study Group standards, represents the safer default strategy and should be adopted where available [13].

The clinical stakes of failing to anticipate an NRLN are substantial. A recent systematic review and meta-analysis reported a pooled NRLN injury risk of 7%, a risk ratio of 3.8 compared with a normal recurrent laryngeal nerve [17]. In the original Toniato series, 12.9% of patients with an NRLN had a postoperative vocal cord deficit, with most injured nerves arising above the laryngotracheal junction and running with the superior thyroid vessels — analogous to type 1 nerves [3]. These figures compare unfavorably with reported nerve palsy rates of roughly 1–4% in benign thyroid surgery overall [18], and IONM use has been associated with a reduction in permanent (though not necessarily early) postoperative palsy [19]. The favorable voice outcome in our patient reflects careful anatomic dissection, but the elevated baseline risk associated with an unanticipated NRLN reinforces the case for a structured, anticipatory approach rather than reliance on intraoperative vigilance alone.

Finally, we note that the NRLN literature is dominated by case reports and series involving multinodular goiter or thyroid malignancy; reports in the specific context of Graves’ disease are essentially absent. The closest disease-matched reports we identified describe a toxic multinodular goiter [20] and a mixed surgical series in which toxic goiter/Graves’ disease accounted for a minority of NRLN-screened cases [21]. Hyperthyroid, Graves’-affected glands are typically larger, more friable, and considerably more vascular than euthyroid glands, which may compound the technical difficulty of nerve identification and increase the consequences of an unanticipated NRLN. To our knowledge, this report represents one of the first cases specifically describing a right NRLN with associated ARSA encountered during total thyroidectomy performed for Graves’ disease, and we believe it adds a clinically relevant data point to a sparsely documented intersection of thyroid pathology and surgical anatomy.