Overview
The equine trachea starts at the cricoid cartilage of the larynx and runs along the ventral neck to the thoracic inlet; in the mediastinum it heads for the base of the heart and divides into the right and left principal bronchi. Its lumen is wide and slightly flattened dorsoventrally.
Structure and relations
- Cartilages: many C-shaped hyaline rings, open dorsally. Their ends overlap cranially and, caudally, are bridged by a membranous band carrying the trachealis muscle.
- Bronchi: the horse has no tracheal bronchus; both principal bronchi arise at the bifurcation, over the base of the heart.
- Relations in the neck: the oesophagus lies dorsal to the trachea in the cranial third of the neck and then moves to its left side. The common carotid artery, the vagosympathetic trunk and the recurrent laryngeal nerve run laterally; the sternothyrohyoideus and sternocephalicus muscles lie ventrally.
- Thyroid: its two lobes rest on the first tracheal rings, caudal to the larynx.
Clinical relevance
- Endoscopy: shows mucus, pus or blood in the tracheal lumen. After strenuous exercise, blood in the trachea indicates exercise-induced pulmonary haemorrhage; mucus scoring is part of the work-up of equine asthma.
- Tracheal wash: a lower airway sample is collected endoscopically or with a transtracheal needle in the middle third of the neck, for cytology and culture.
- Emergency tracheotomy: in upper airway obstruction the trachea is opened on the ventral midline, at the junction of the cranial and middle thirds of the neck, by separating the sternothyrohyoideus muscles and cutting between two rings.
- Tracheal collapse: dorsoventral flattening of the rings, described mainly in ponies and miniature horses; it causes respiratory noise and exercise intolerance.