Aberrant left pulmonary artery

An aberrantAberrant left pulmonary artery (or, also known as pulmonary sling) represents, represents an anatomical variant thatcharacterised by the left pulmonary artery arising from the right pulmonary artery and passing above the right main bronchus and in between the trachea and oesophagus to reach the left lung. It may result in symptoms because oflead to compression ofand local structures, in particular, of the trachea.

Pathology

Aberrant left pulmonary arteries are thought to arise from a failure of formation of the 6^th aortic arch. They have an anomalous origin from the posterior wall of the right pulmonary artery before coursing to the left lung passing posterior to the trachea and anterior to the oesophagus. 

The term “sling” is best used when the proximal portion of the anomalous vessel impinges on the right main bronchus and causes air trapping of the entire right lung, or right middle or lower lobes. 

The second type of aberrant left pulmonary artery, which often is fatal, is associated with long-segment tracheal stenosis. This typekind of tracheal stenosis is due to complete tracheal rings. 

Associations

Other anomalies that can be associated with aberrant left pulmonary artery are:

• head and neck
  • absent thyroid isthmus
• thoracic
  • complete tracheal rings
  • tracheal stenosis
  • single lobed left lung
  • bilobed right lung
  • congenital lobar overinflation ⁵
• abdominopelvic
  • imperforate anus
  • Hirschsprung disease
  • intestinal malrotation
  • agenesis of left kidney and ureter
  • agenesis of gallbladder
• musculoskeletal
  • fusion of third and fourth lumbar vertebrae
  • diaphragmatic hernia

Radiographic features

Plain radiograph

Conventional radiographs obtained in neonates at birth may show fetal fluid retention or air, with a mediastinal shift usually to the left side.

In adults, a left-sided deviation of the trachea and an anterior bowing of the right main stem bronchus may be seen.  In cases of ring sling complex, conventional radiographs often show an absence of unilateral pulmonary aeration. 

Fluoroscopy

In most instances, the barium oesophagogram characteristically shows a mass between the trachea and the oesophagus just above the level of the carina, usually seen as an anterior indentation over the oesophagus. 

CT/MRI

The main bronchi have horizontal courses (i.e. low T-shaped carina), and vascular anatomy is normally well delineated on CT or MR angiography. Atelectasis may be seen in the upper lobes. 

Treatment and prognosis

Repositioning of the artery usually reverses compression, particularly when the underlying tracheobronchial tree is normal. 

The mortality rate is high in patients requiring tracheal reconstruction because the stenosis is primary and not due to the vessel.

The success of reconstructive procedures in the rigid trachea can be studied by using three-dimensional CT techniques such as virtual bronchoscopy.