title: Upper airway dysfunction associated with collapse of the apex of the corniculate process of the left arytenoid cartilage during exercise in 15 horses.
abstract: OBJECTIVE
  To report dynamic collapse of the apex of the left corniculate process under the right corniculate process into the airway at the dorsal apposition of the paired arytenoid cartilages during exercise as a cause of upper airway dysfunction in horses.
  
  
  METHODS
  Retrospective study.
  
  
  METHODS
  Fifteen horses with a history of poor performance and/or upper respiratory tract noise during exercise.
  
  
  METHODS
  Video recordings of all horses referred for upper airway evaluation using high-speed treadmill videoendoscopy (HSTV) between January 1998 and December 2003 were reviewed. Records of horses that developed dynamic collapse of the apex of the left corniculate process into the airway were included. Clinical history, age, gender, breed, and use of the horse were retrieved.
  
  
  RESULTS
  Of 309 horses referred for examination for poor performance and/or upper respiratory tract noise during exercise, 15 (4.9%) had collapse of the apex of the left corniculate process under the right and into the airway at the dorsal apposition between the paired arytenoid cartilages during HSTV. There were 3 females and 13 males, aged from 2 to 5 years. Five horses had previous surgery for left recurrent laryngeal neuropathy (RLN): 2 had nerve muscle pedicle graft and 3 had laryngeal prosthesis. During HSTV, all 15 horses had progressive collapse of the apex of the left corniculate process under the right at the dorsal apposition of the 2 arytenoid cartilages, and into the dorsal aspect of the rima glottidis. Review of video recordings revealed that collapse of the apex of the corniculate process was followed by progressive collapse of the left aryepiglottic fold and left vocal fold. The ventral aspect of the left corniculate cartilage maintained abduction in all horses. Two horses also had progressive collapse of the right vocal fold, 1 had rostral displacement of the palatopharyngeal arch, and another had dorsal displacement of the soft palate.
  
  
  CONCLUSIONS
  Dynamic collapse of the apex of the left corniculate process of the arytenoid cartilage under the right is an uncommon cause of upper airway dysfunction in horses and the pathogenesis is unclear. We speculate that the left arytenoideus transversus muscle is unable to support the dorsal apposition between the arytenoid cartilages. This loss of support allows the elastic cartilage of the left corniculate process to collapse under the right and into the airway, as inspiratory pressure increases during exercise. This condition may be associated with an unusually advanced neuropathy of the adductor components of the left recurrent laryngeal nerve and may be an unusual manifestation of RLN; however, this is speculative and further investigation is required to determine its cause.
  
  
  CONCLUSIONS
  Dynamic collapse of the apex of the left corniculate process and into the airway at the dorsal apposition between the paired arytenoid cartilages can only be diagnosed during HSTV. It is an uncommon cause of upper airway dysfunction but may affect the athletic potential of racing Thoroughbreds and Standardbreds.
authors.affiliation: Faculty of Veterinary Science, The University of Sydney, New South Wales, Australia. andrewd@camden.usyd.edu.au
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Dart
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Dowling
authors.forename: Christine L
authors.initials: CL
authors.lastname: Smith
mesh_terms: D000818:Animals; D001193:Arytenoid Cartilage / Q000502:physiology / Q000503:physiopathology*; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis / Q000473:pathology*; D006736:Horses; D008297:Male; D010805:Physical Conditioning, Animal; D012140:Respiratory Tract Diseases / Q000175:diagnosis / Q000473:pathology / Q000662:veterinary*; D012189:Retrospective Studies; D013906:Thoracoscopy / Q000662:veterinary; D014741:Video Recording