Teaching Case

A female patient, aged 42 and a former smoker (20 pack units/year), presented with dyspnoea and a sensation of thoracic pain since childhood with worsening during adolescence. At physical examination she presented an asymmetrical thorax, with diminished murmur on the right hemithorax. Echocardiogram and spirometry were normal.

A chest radiogram was performed which showed asymmetry of the lung fields, with decreased right lung volume, right mediastinal shift and left hyperinflated and hyperlucent lung (Figure 1). There were no relevant changes to the diaphragm and no pleural effusion.
The patient then underwent a contrast-enhanced chest CT with multiplanar and volume reconstructions. On lung window settings, the CT showed a small right lung, with deviation of the mediastinum ipsilaterally and hyperinflation of the left lung, along with moderate centrilobular emphysema with a right lower lobe predominance, discrete tubular bronchiectasis and very discrete mosaic pattern on the inferior lobe of the right lung (Figure 2). The most important finding on the contrast enhanced arterial phase was the proximal interruption of the right pulmonary artery, with a normal caliber main pulmonary artery, and paucity of vessels in the right lung (Figures 3 and 4).

The proximal pulmonary artery is derived from the sixth aortic arch [1]. The unilateral interruption of a pulmonary artery is a rare disease (1 in 200, 000-300, 000 adults) that can be congenital or acquired, isolated or associated with other cardiovascular anomalies [1].
It is usually associated with a hypoplastic ipsilateral lung with normal bronchial tree development [2]. It most commonly affects the right side (60%), although it is most commonly associated with congenital heart diseases (80%) when the left side is affected [1-3].
In childhood it usually presents with congestive heart disease and pulmonary hypertension, while in adults it tends to remain asymptomatic or be associated with exercise intolerance, hemoptysis and recurrent respiratory infections [1-5]. Pulmonary hypertension, though scant, is an important prognosis determinant of the disease [3, 4].
The diagnosis is based on medical history, physical examination and imaging, this last being key to demonstrate the absence of the pulmonary artery, namely on cross sectional imaging [1, 3, 4, 6, 7].
On the thoracic radiogram, asymmetrical lung fields are usually observed, with an ipsilateral small and hypolucent hemithorax, a mediastinal shift towards the affected side, an elevated ipsilateral hemidiaphragm and diminished or absent ipsilateral vasculature [3, 5-10], all of which were present in our case.
The computed tomography (CT) and magnetic resonance (MR) usually show an absent pulmonary artery or terminating within 1 cm of its expected origin [2, 3, 10, 11], with associated findings such an hypoplastic lung [10], mediastinal ipsilateral shift with bronchiectasis, mosaic parenchymal pattern, variable collateral circulation and peripheral branches of the pulmonary artery [2, 8, 9].
Angiography is the gold standard of diagnosis, though it is currently used only in cases where the cross sectional imaging findings are equivocal [1, 11]. In our case, the diagnosis was straightforward after the performance of the chest CT, so no angiography was performed.
There is no consensus regarding treatment and it is mainly symptomatic [1]. In childhood pulmonary artery anastomosis or aorto-pulmonary shunts can be surgically created, and when a surgical approach is being considered imaging is of the utmost importance to assess for collaterals. The treatment is usually reserved for patients with hemoptysis, recurrent respiratory infections and pulmonary hypertension, with treatment options of partial or total pneumectomy or selective embolization in the case of massive hemoptysis [1, 2].
The imaging findings are essential for this diagnosis, most importantly sectional imaging, as these methods allow for a confident statement of the absence or proximal interruption of a pulmonary artery.