Teaching Case

A 25-year-old male with history of heavy smoking for 10 years, presented initially with mild breathlessness on exertion. A chest radiograph was performed but the patient failed to return for consultation. 6 months later the patient returned with a history of mild haemoptysis. A contrast-enhanced CT chest was performed.

Chest radiograph revealed signs of loss of right lung volume with ipsilateral mediastinal shift. Suggestion of reduced lung markings was also noted on the right side with hyperinflation of the left lung, likely compensatory in nature. Apparent widening of the right paratracheal stripe was seen, later proven to be normal mediastinal vascular structures on CT.
Contrast-enhanced CT showed complete absence of the right pulmonary artery and its branches, reduced right lung volume and mediasitnal shift to the right side. Multiple small vascular collaterals were seen surrounding the carina and along the right pleural surface with an enlarged right internal mammary artery, contributing to right lung blood supply. Lung window images revealed, subpleural and fissural nodularity in right lung due to vascular collaterals, mimicking interstitial lung disease. Mild emphysematous changes were also seen in right middle and lower lobe.

Unilateral agenesis of the pulmonary artery(UAPA) is a rare congenital anomaly that occurs due to an abnormality involving the development of the sixth aortic arch [1]. A prevalence of about 1 in 200000 young adults is suggested [3]. Right sided agenesis appears more frequent. Other congenital cardiac abnormalities may be associated, however are more commonly seen with left sided agenesis [2].
Median age at diagnosis is about 14 years, however many cases present during adulthood [1, 4]. Common presenting symptoms include dyspnoea, recurrent chest infections and reduced exercise tolerance. Haemoptysis has been reported in 10-20% of patients [1, 2]. Pulmonary hypertension occurs in about 25-44% of cases and affects survival [1, 3]. UAPA is commonly not considered during routine clinical examination. Unilateral reduced air entry and a mild restrictive pattern on pulmonary function tests may be the only clues [1]. Chest radiograph is often the first modality to raise suspicion of the condition.
Chest X-Ray shows ipsilateral mediastinal shift and elevated hemidiaphragm with non visualisation of the pulmonary artery shadow and contralateral hyperinflation [1, 2, 3]. Abnormal mediastinal rotation may mimic mediastinal lesions, as in our case. In the past, conventional pulmonary angiography confirmed the diagnosis, however in recent times contrast CT has emerged as the modality of choice. The primary CT finding is cut-off of the right or left branch of the pulmonary artery within 1 cm of its origin. Loss of ipsilateral lung volume, mediastinal shift and contralateral hyperinflation are also clearly visualised. Mosaic perfusion, emphysematous changes and bronchiectatic changes may be seen in both lungs due to compensatory changes or recurrent infections. The prominent transpleural collaterals may cause subpleural and fissural nodularity and mimic infection on Chest X-ray or interstitial lung disease on CT, as was seen in our case. Signs of systemic collateral circulation, pulmonary hypertension and associated cardiac anomalies are elegantly depicted on contrast CT [1, 2, 3]. MRI may also be used to diagnose absence of the pulmonary artery branch.
UAPA has a mortality rate of about 7 %. Prognosis is negatively affected by pulmonary hypertension and pulmonary haemorrhage. Surgical revascularisation of maintained peripheral pulmonary vasculature to hilar vessels has been tried successfully in paediatric cases. Embolisation is used to control haemorrhage. Pneumonectomy is reserved for cases of recurrent haemoptysis or recurrent infections [1, 3].