Introduction

• Cause:
  • Uncommon condition; primary tracheal collapse → obstruction of the tracheal lumen due to dorsoventral flattening of trachea probably caused by abnormal cartilage matrix in ponies and miniature horses.
  • Secondary tracheal collapse → obstruction of the tracheal lumen secondary to trauma or compression by extraluminal causes, or collapse of the cricotracheal ligament (CTLC) reducing the airway diameter where the cricoid cartilage connects to the trachea.
• Signs: respiratory stridor, dyspnea, cyanosis, poor performance.
• Diagnosis: endoscopy and radiography.
• Treatment: depends on cause and severity; treat underlying cause; conservative therapy; surgical correction.
• Prognosis: fair if normal tracheal lumen size and shape is restored.

Pathogenesis

Etiology

Primary collapse

• Paresis of the trachealis muscle.
• Mineralization of the tracheal cartilages.
• Defective tracheal cartilage.
• Slack and elongated dorsal tracheal ligament.
• Lower airway disease creating abnormal negative pressure, eg RAO, SPAOPD, bacterial pneumonia.

Secondary collapse

• Trauma resulting in tracheal damage.
• Extraluminal compression, eg neoplasia.

Collapse of the cricotracheal ligament

• Thought to result from a congenitally abnormally wide space between the cricoid cartilage and the 1st tracheal ring.
• Or, as a result of abnormally increased negative pressure within the trachea during exercise.

Predisposing factors

Specific

• Primary tracheal collapse: lower airway disease creating abnormal negative pressure.
• CTLC: all reported cases have concurrent pharyngeal lymphoid hyperplasia.

Pathophysiology

• Primary tracheal collapse: cartilage defect (failure of normal glycosaminoglycans and glycoprotein synthesis) → structurally weaker matrix (demonstrated in dogs).

Timecourse

• Primary tracheal collapse is often intermittent initially and may be associated with stressful events, exercise, dusty environment and eating, but the severity of clinical signs often increases over time.

Diagnosis

Treatment

Prevention

Outcomes