Non-recurrent laryngeal nerve with dual branch pattern and merging: a rare anatomical variant encountered during...

The non-recurrent laryngeal nerve (NRLN) is an uncommon anatomical variant that passes directly from the vagus nerve to the larynx without the usual recurrent loop; it occurs on the right side in around one in a hundred individuals and is considerably rarer on the left. Its recognition is central to safe thyroid surgery, because an unanticipated NRLN lies in an unexpected position and is vulnerable to inadvertent injury. We report a right non-recurrent laryngeal nerve with an unusual dual-branch morphology in which the nerve divided and then re-merged before laryngeal entry.

A woman in her 50s underwent right hemithyroidectomy for a benign, compressive multinodular goitre of the right lobe. Intraoperatively, no recurrent laryngeal nerve was found in the expected tracheo-oesophageal groove; systematic tracing of the vagus nerve within the carotid sheath revealed a right NRLN that divided into a superior and an inferior branch. The two branches followed separate courses and re-merged into a single trunk approximately 10 mm before entering the larynx through the cricothyroid membrane. Both branches were identified and preserved. The patient was extubated uneventfully, demonstrated normal vocal cord function, and made an uncomplicated recovery with no voice change at early or later follow-up.

Dual-branch NRLN in which the branches re-merge before laryngeal entry is a pattern we have not found previously described; while extra-laryngeal division of a non-recurrent nerve has been reported, the subsequent re-merging adds complexity to nerve identification and preservation. Awareness that a non-recurrent nerve may branch and re-merge should prompt complete tracing of every fascicle followed from the vagus during thyroid surgery.