Isolated unilateral absence of pulmonary artery

Isolated unilateral absence of the pulmonary artery (IUAPA) is the congenital absence of the left or right pulmonary artery. When found in combination with other congenital vascular abnormalities it is known as unilateral absence of the pulmonary artery (UAPA).

Epidemiology

Unilateral absence of the pulmonary artery is a rare clinical condition affecting <0.3% of the population. Isolated unilateral absence pulmonary artery accounts for 40% of such cases. 

Associations

Whilst isolated unilateral absence of the pulmonary artery is not associated with other clinical conditions, unilateral absence of the pulmonary artery may be associated with the following vascular abnormalities:

• tetralogy of Fallot

• coarctation of the aorta

• ventricular septal defect (VSD)

• subvalvular aortic stenosis

• transposition of the great arteries (plus VSD or pulmonary stenosis)

• Taussig-Bing malformation and coarctation

• congenitally corrected transposition and pulmonary stenosis

• scimitar syndrome

Clinical presentation

Isolated unilateral absence of the pulmonary artery is often associated with congenital heart conditions and usually diagnosed in early childhood. It may also present in adults with the following symptoms:

• dyspnoea

• reduced exercise tolerance

• chest pain

• pleural effusion

• recurrent bronchopneumonia

• haemoptysis

• high-altitude pulmonary oedema (HAPE)

• respiratory difficulty during pregnancy

• asymptomatic and found incidentally (30%)

Pathology

Isolated unilateral absence of the pulmonary artery is thought to be due to failed migration and rotation of the primitive sixth aortic arch resulting in agenesis of the pulmonary artery.

The pathogenesis of recurrent bronchopneumonia is thought to be due to hypoperfusion, V-Q mismatch, reduced mucosal defence, and possibly protease-antiprotease imbalance. Haemoptysis is caused by excessive collateral circulation.

Radiographic features

Plain radiograph

• ipsilateral contracted lung / small hemithorax

• mediastinal and tracheal shift toward the affected side

• ipsilateral hemidiaphragm elevation

• absent hilar shadow / pulmonary artery

• ipsilateral diminished pulmonary vascular markings

• contralateral lung hyperinflation and prominent pulmonary artery

• absent air trapping on expiratory film

Echocardiography

• absence of the artery

• pulmonary hypertension

• associated cardiac anomalies

CT/MRI

• diminished pulmonary vessels

• ipsilateral hypertrophy of collateral vasculature

• bronchiectasis secondary to recurrent bronchopneumonia

Angiography (DSA)

• absence of the pulmonary artery

• presence of the pulmonary trunk and contralateral pulmonary artery

Right heart catheterisation

• pulmonary capillary wedge pressure

• pulmonary capillary wedge angiography (looking for hidden hilar arteries)

Nuclear medicine

On V-Q scintigraphy (quantitative):

• absent perfusion to the affected side

• useful for distinguishing isolated unilateral absence of the pulmonary artery from Swyer-James-McLeod syndrome

Treatment and prognosis

Treatment options include:

• revascularisation surgery

• pulmonary vasodilator therapy (for pulmonary hypertension)

• pneumonectomy or lobectomy

• embolisation of collateral haemorrhage

Pulmonary hypertension and haemoptysis confer a poorer prognosis.

Complications

• pulmonary hypertension

• right heart failure

• bronchiectasis

• high altitude pulmonary oedema

• pulmonary haemorrhage

Differential diagnosis

On imaging consider:

• pulmonary embolus

• Swyer-James-MacLeod syndrome

• primary pulmonary hypertension