Non-recurrent Laryngeal Nerve - A Rare Anatomical Anomaly that Increases the Risk of Nerve Injury during Thyroidectomy.

Introduction: Nonrecurrent laryngeal nerve (NRLN), a rare anatomical variation of recurrent laryngeal nerve, is a branch of the vagus nerve (Morais M, Capela-Costa J, Matos-Lima L, Costa-Maia J (2015) Nonrecurrent Laryngeal Nerve and Associated Anatomical Variations: The Art of Prediction. Eur Thyroid J 4(4):234-238). On the right side, the prevalence of NRLN is 0.3-0.8%, while on the left side, it is extremely rare with a prevalence of 0.004%.

Case-report: A female in her twenties presented with thyroid swelling for 3 years with an ultrasound neck showing a TIRADS IV lesion in the left thyroid lobe. Contrast-enhanced tomography of the neck reported a lesion in the left thyroid lobe causing mass effect in the form of contralateral deviation of trachea and splaying of bilateral common carotid arteries from its common origin - probability of thyroid neoplasm along with aberrant right subclavian artery with a retroesophageal course was noted. Intraoperatively, the right laryngeal nerve was identified near its entry point in right cricothyroid joint and was traced laterally and was found to be nonrecurrent lying superior to inferior thyroid artery. Total thyroidectomy was done preserving the left recurrent laryngeal nerve and right non recurrent laryngeal nerve.

Conclusion: NRLN should be suspected in cases with vascular anomalies based on preoperative imaging. Meticulous dissection during thyroid surgery for identification of the recurrent laryngeal nerve or NRLN is still considered to be the precise approach to avoid nerve injury.