Pulmonary Artery Sling

Pulmonary artery sling is a rare anomaly in which the left pulmonary artery arises from the right pulmonary artery instead of the main pulmonary trunk.

It then runs over the right main bronchus and between the trachea and oesophagus to reach the left hilum, forming a sling that compresses the distal trachea and right main bronchus. About half of patients have complete tracheal rings with long segment tracheal stenosis (the ring sling complex).

Other associations are bridging bronchus, right lung hypoplasia, and cardiac lesions (atrial septal defect, ventricular septal defect, patent ductus arteriosus, persistent left superior vena cava) in about half. It represents under 0.5% of congenital heart disease.

Pathophysiology. The sling and any intrinsic tracheal stenosis cause fixed airway obstruction with air trapping, unilateral hyperinflation or collapse. The retro tracheal, pre-oesophageal course explains the characteristic oesophageal indentation.

Presentation is usually in the first weeks to months of life:

• Stridor (expiratory or biphasic), wheeze that does not respond to bronchodilators, brassy cough, respiratory distress
• Apnoeic or cyanotic spells, recurrent chest infections, feeding difficulty, failure to thrive
• Ring sling complex: severe airway obstruction from birth
• Milder cases may reach later childhood or adulthood

Red flags.

• Severe respiratory distress, apnoea or cyanotic spells in the first weeks
• Stridor with failure to thrive
• Suspected tracheal rings
• Difficulty passing an endotracheal tube of the expected size

• Chest X-ray: unilateral hyperinflation (usually right) or collapse.
• Barium swallow: an anterior indentation of the oesophagus. This is the only vascular anomaly that indents it from the front.
• Echocardiography: left pulmonary artery arising from the right pulmonary artery, and associated cardiac lesions.
• CT angiography with airway reconstruction: the key test. It defines the sling, tracheal stenosis, tracheal length, bridging bronchus and lung hypoplasia.
• Flexible bronchoscopy: complete cartilage rings with absent posterior membrane, and tracheomalacia. Perform with an experienced airway team because airway manipulation can precipitate complete obstruction.

Differential diagnosis.

• Other vascular rings (double aortic arch, right arch with left ligamentum arteriosum)
• Innominate artery compression
• Primary tracheomalacia
• Subglottic stenosis
• Laryngomalacia
• Bronchiolitis or asthma
• Foreign body
• Congenital lobar emphysema
• Mediastinal mass

• Surgery is indicated for symptomatic patients. Reimplant the left pulmonary artery into the main pulmonary trunk through a median sternotomy on cardiopulmonary bypass, with repair of associated cardiac lesions. When tracheal stenosis is severe, tracheoplasty (slide tracheoplasty) is done in the same operation.
• Mild asymptomatic sling without airway compromise: observation with periodic imaging.
• Perioperative airway: humidified oxygen, avoid unnecessary airway instrumentation, and use the smallest endotracheal tube that provides ventilation, because the stenotic segment can be fixed.
• Complications: left pulmonary artery stenosis or thrombosis, residual tracheomalacia, airway granulation and stenosis.

Special groups. Infants with ring sling complex carry a higher mortality and need staged airway care in a centre with tracheal surgery experience.

Monitoring. Echocardiography for left pulmonary artery patency at 1 and 6 months, then yearly, with CT when stenosis is suspected. Bronchoscopy at 6 to 12 months or if symptoms persist. Growth and feeding review.

Referral and escalation. Refer to a paediatric cardiothoracic centre with airway surgery. Urgent for apnoea, cyanosis or respiratory failure.