title: Distance between Anterior Commissure and the First Tracheal Ring: An Important New Clinical Laryngotracheal Measurement.
abstract: BACKGROUND
  The distance between the anterior commissure of the larynx and the first tracheal ring (AC.T. distance) is of great importance in laryngotracheal surgeries. The amount of narrowing of the subglottic airway is used as a quantitative mean to determine whether the lesion is subglottic or has extended to the trachea and therefore helps in the prediction of the final prognosis.
  
  
  METHODS
  In this study, the larynx was exposed by direct laryngoscopy under general anesthesia. The case was considered to be difficult because the exposure did not optimally reveal the anterior commissure, therefore a cricoid tape or anterior commissure laryngoscope was used. A zero degree Hopkins lens was used to view the anterior commissure and the first tracheal ring. Special markers were used to mark the two points with the distance between those being considered as the AC.T. distance. The relationship between AC.T. distance and the patient's age, sex, BMI, and laryngeal exposure condition during laryngoscopy was also studied.
  
  
  RESULTS
  Eighty-two patients participated in this study. The mean AC.T. distance was measured and was found to be 32.67±3.34 mm in males and 29.80± 3.00 mm in females. This difference was statistically significant between the two groups (P<0.05). There was no statistically significant relationship between BMI, age, laryngeal exposure condition, and the AC.T. distance.
  
  
  CONCLUSIONS
  The AC.T. distance was measured to be around 3 cm; with males measuring greater than females. However, future studies may lead to a more accurate practical scale for laryngotracheal surgeries due to possible technical or human errors, in addition to racial differences.
authors.affiliation: Sinus and Surgical Endoscopic Research Center, Ghaem Hospital, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Khadivi
authors.affiliation: Department of Otorhinolaryngology-Head & Neck Surgery, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Zaringhalam
authors.affiliation: Department of Otorhinolaryngology-Head & Neck Surgery, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Kamran
authors.initials: K
authors.lastname: Khazaeni
authors.affiliation: Sinus and Surgical Endoscopic Research Center, Ghaem Hospital, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Bakhshaee
keywords: Airway stenosis; Anterior commissure; BMI; Subglottic; Trachea; Vocal cord