title: The anatomy of the external branch of the superior laryngeal nerve in Koreans.
abstract: BACKGROUND
  Preservation of the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy is important because its injury may lead to frequent occurrence of vocal fatigue and the inability to perform superenergetic phonation. Most studies on the anatomy of EBSLN have been performed in Western countries and, thus, have some limitations in their application to Koreans. We explored the anatomy of EBSLNs using intraoperative neuromonitoring (IONM) in Korean adults.
  
  
  METHODS
  Between August 2011 and December 2011, 50 patients underwent thyroidectomy at Korea University, Anam Hospital in Seoul, Korea. IONM was performed with the NIM response 3.0 system.
  
  
  RESULTS
  Forty-two total thyroidectomies and eight lobectomies were performed with IONM and 92 EBSLNs were evaluated. Type I EBSLN was observed in 15 of the 92 nerves (16.3%), type IIa EBSLN was noted in 52 (56.5%) and type IIb EBSLN was noted in 25 (27.2%). Patients with types IIa and IIb were at higher risk of injuries and these types were more frequently observed (83.7%) compared with previous Western studies. We found that 35.9% of distal insertion sites of EBSLNs were located within 1cm of the center of the cricoid cartilage.
  
  
  CONCLUSIONS
  Surgeons should pay close attention to preserving the EBSLN during thyroidectomy in Korean patients because their EBSLNs are more frequently located beneath the superior thyroid vessels.
authors.affiliation: Division of Breast-Thyroid Surgery, Department of Surgery, Hansarang Hospital, Ansan, Republic of Korea.
authors.forename: Seong-Bae
authors.initials: SB
authors.lastname: Hwang
authors.forename: Hye-Yoon
authors.initials: HY
authors.lastname: Lee
authors.forename: Woo-Young
authors.initials: WY
authors.lastname: Kim
authors.forename: Sang-Uk
authors.initials: SU
authors.lastname: Woo
authors.forename: Jae-Bok
authors.initials: JB
authors.lastname: Lee
authors.forename: Jeoung-Won
authors.initials: JW
authors.lastname: Bae
authors.forename: Hoon-Yub
authors.initials: HY
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D044466:Asian People; D003431:Cross-Cultural Comparison; D005260:Female; D006801:Humans; D064795:Intraoperative Neurophysiological Monitoring; D061224:Laryngeal Nerve Injuries / Q000503:physiopathology / Q000517:prevention & control; D007823:Laryngeal Nerves / Q000033:anatomy & histology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D056910:Republic of Korea; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000601:surgery; D013965:Thyroidectomy