Non-recurrent laryngeal nerve in thyroid and parathyroid surgery

Abstract

BACKGROUND : the main reason for postoperative vocal folds paresis is the variable anatomy of the recurrent laryngeal nerve. An example of such an “extreme form of embryonal development» is the non-recurrent laryngeal nerve. However, many surgeons consider this structure to be a rare anomaly with prevalence less than 0.5%. This opinion is associated with a six to seven-fold increase in the number of vocal folds paresis when a surgeon encounters with a non-recurrent laryngeal nerve. Meanwhile, in cadaveric studies a significantly higher prevalence of non-recurrent laryngeal nerve was demonstrated — 2.2%. The right aberrant subclavian artery was diagnosed during CT in 3.1% patients. AIM : the aim of the study is to determine the effectiveness of preoperative ultrasound in detecting the right aberrant subclavian artery and non-recurrent laryngeal nerve. MATERIALS AND METHODS : patients underwent thyroid and parathyroid surgery with identification of a right inferior laryngeal nerve. The preoperative neck ultrasound was performed on all patients with visualization of a brachiocephalic trunk (Y-sign) or a right aberrant subclavian artery (AL-sign). CT-angiography was performed in the postoperative period on patients who had a non-recurrent laryngeal nerve. RESULTS : the study included 1476 patients. The Y-sign was determined among 1338 (90.7%) patients. In these cases a typical anatomy of the recurrent laryngeal nerve was observed. In 138 (9.3%) cases, the Y-sign was not detected. In this subgroup of patients, in 20 (1.4%) cases, a non-recurrent laryngeal nerve and a right aberrant subclavian artery were noted. Thus, the sensitivity of the Y-sign in confirming the normal anatomy of the recurrent laryngeal nerve was 100%, specificity — 91.9%, positive prognostic value — 14.5%, negative prognostic value — 100%. On the contrary, AL-sign was notedall 20 (1.4%) patients with non-recurrent laryngeal nerve and right aberrant subclavian artery. False positive and false negative results were not observed. Three variants of the non-recurrent laryngeal nerve were identified: type I (superior type) — located behind the upper third of the thyroid lobe, has a direct descending way and forms an angle to the larynx of 30–50°; type III (inferior type) — has a direct ascending way (simulates the course of the recurrent laryngeal nerve) and forms an angle to trachea in 30–50°; type II (middle type) — all variants of the non-recurrent laryngeal nerve located between types I and III. CONCLUSION : the preoperative ultrasound detection of brachiocephalic trunk (Y-sign) confirms the presence of a recurrent laryngeal nerve (sensitivity 100%), and visualization of the right aberrant subclavian artery (AL-sign) determines a non-recurrent laryngeal nerve (sensitivity and specificity 100%).