Teaching Case

An 8-year-old boy was admitted to the emergency department of our hospital with reported injury of chest and abdomen after a bike accident. No significant clinical findings of trauma or other pathology were ascertained. Laboratory results were normal. Plain chest and abdomen radiographs were initially obtained.

Chest X-ray revealed a significant shift of the mediastinum towards the right. Thus, a chest CT was performed followed by CT angiography. An important shift of the mediastinum towards the right and hyperinflation of the left lung was demonstrated. The right lung had lost volume, but its lobar and segmental anatomy appeared normal. The mediastinal portion of the Right Pulmonary Artery (RPA) was absent. The interlobar portion of the RPA and small intrapulmonary peripheral vessels were depicted but they appeared small comparatively with the contralateral portion of the Left Pulmonary Artery (LPA). In the right hilum area multiple vascular structures were also depicted, probably representing dilated bronchial arteries of collateral circulation. LPA and its branches appeared with increased width. Lung parenchyma appeared normal.

Proximal interruption of the pulmonary artery is a rare congenital condition with prevalence 1/200.000 [1, 2]. Usually interruption of the pulmonary artery exists contralateral to the aortic arch [2, 3]. Thus, the most common type is interruption of the RPA as an isolated finding with a 63% rate followed by interruption of the LPA with co-existing right aortic arch or tetralogy of Fallot [2-5]. Embryologically, the proximal part of one of the two branches of the main pulmonary artery is not developed due to an anomaly of the sixth branchial arch [3, 6].

Patients with proximal interruption of RPA are divided by Bahler et al. [5]:
a. patients with left-to-right shunt (usually patent ductus arteriosus)
b. patients with associated pulmonary hypertension
c. patients without pulmonary hypertension.
Categories a. and b. have low survival rates after infancy[7]. Category c. patients are usually incidentally diagnosed, in a mean age of 14 years [2, 7]. Other symptoms may be: haemoptysis, recurrent pulmonary infections and dyspnoea. Pulmonary haemorrhage induced by rupture of collateral vessels occurs rarely [8].

Chest X-ray shows volume loss of the affected lung including elevation of the hemidiaphragm and shift of the mediastinum and heart to the ipsilateral side. The hilum in the affected side is indistinct. Collateral intercostal circulation may develop, resulting in pleural thickening and rib notching, with an associated fine reticular pattern in the lung peripherally. The contralateral lung hyperinflates and herniates towards to the affected side. The hilum of the contralateral side is enlarged as the entire output of the right ventricle arrives there [3, 7, 9, 10].

Diagnosis is set with chest CT angiography. The mediastinal portion of RPA is clearly demonstrated and is usually absent or terminated in 1cm from its origin. LPA and its divisions appear prominent. Hypertrophied intercostal, bronchial, internal mammary, subclavian and innominate arteries may be identified (collateral circulation). Consequently, rib notching and pleural thickening may be seen. The bronchial branching pattern of the affected small lung remains normal. There is often an appearance of mosaic attenuation on both lungs, related to hypoxic vasoconstriction in the affected lung and to over-perfusion of the unaffected lung [3, 7, 9, 10].

Asymptomatic patients are closely followed-up and in cases of massive haemoptysis and arterial hypertension are treated surgically with systemic embolisation and revascularisation of the interrupted pulmonary artery, respectively [2, 8, 9]. In our case, a heart ultrasound was performed in order to exclude other co-existing heart anomalies. Finally, instructions were given and regular follow-up was scheduled.