title: Surgical anatomy of bilateral extralaryngeal bifurcation of the recurrent laryngeal nerve: similarities and differences between both sides.
abstract: BACKGROUND
  Anatomical variations of the recurrent laryngeal nerve (RLN) such as extralaryngeal terminal bifurcation is an important risk for its motor function.
  
  
  OBJECTIVE
  The objective is to study surgical anatomy of bilateral bifurcation of the RLNs in order to decrease risk of vocal cord palsy in patients with bifurcated nerves.
  
  
  METHODS
  Surgical anatomy including terminal bifurcation was established in 292 RLNs of 146 patients. We included patients with bilateral bifurcation of RLN in this study. Based on two anatomical landmarks (nerve-artery crossing and laryngeal entry), the cervical course of RLN was classified in four segments: Pre-arterial, arterial, post-arterial and pre-laryngeal. According to these segments, bifurcation point locations along the cervical course of RLNs were compared between both sides in bilateral cases.
  
  
  RESULTS
  RLNs were exposed throughout their entire courses. Seventy (48%) patients had bifurcated RLNs. We identified terminal bifurcation in 90 (31%) of 292 RLNs along the cervical course. Bilateral bifurcation was observed in 20 (28.6%) patients with bifurcated RLNs. Bifurcation points were located on arterial and post-arterial segments in 37.5% and 32.5% of cases, respectively. Pre-arterial and pre-laryngeal segments contained bifurcations in 15% of cases. Comparison of both sides indicated that bifurcation points were similar in 5 (25%) and different in 15 (75%) patients with bilateral bifurcation. Permanent nerve injury did not occur in this series.
  
  
  CONCLUSIONS
  Bilateral bifurcation of both RLNs was observed in approximately 30% of patients with extralaryngeal bifurcation which is a common anatomical variation. Bifurcation occurred in different segments along cervical course of RLN. Bifurcation point locations differed between both sides in the majority of bilateral cases. Increasing surgeons' awareness of this variation may lead to safely exposing bifurcated nerves and prevent the injury to extralaryngeal terminal branches of RLN.
authors.affiliation: Department of Surgery, Duzce University, Medical Faculty, Duzce, Turkey.
authors.forename: Emin
authors.initials: E
authors.lastname: Gurleyik
keywords: Anatomic variation; Nerve injury; Thyroid; Vocal cord palsy