Teaching Case

A 26-year-old man admitted with complaints of three episodes of haemoptysis. No history of fever, chest pain, dyspnoea or syncope.

Chest radiograph showed prominent vessels in the right lower zone. Contrast-enhanced computed tomography (CT) of thorax showed prominent vessels in the right lower lobe which were branches of an anomalous branch of descending thoracic aorta. In addition to these vessels, normal pulmonary vasculature was also supplying the lower lobe. There was no evidence of lung sequestration. Selective angiography revealed distal aneurysmal dilatation of the artery without evidence of early venous drainage. Obliteration of the anomalous artery was achieved by embolization of the distal branches using multiple coils and proximal segment with Amplatzer Vascular Plug.

Bronchopulmonary sequestration includes a spectrum of abnormalities of lung parenchyma characterized by abnormal systemic vascular supply to lung. In 1946, Pryce proposed a classification system encompassing pulmonary sequestration and anomalous systemic arterial supply to lung. It included Pryce type I – normal lung with anomalous systemic arterial supply, type II – anomalous artery supplying sequestered lung and adjacent normal lung, type III – anomalous artery to sequestered lung [1]. Systemic arterialization of lung without pulmonary sequestration (Pryce type I), also referred to as “pseudosequestration”, is the rarest form of anomalous systemic arterial supply to lung [2,3]. It can be of two types: isolated systemic arterial supply to normal lung (ISSNL) and systemic arterial supply associated with normal pulmonary artery (dual supply) [4].

During normal lung development, the early lung bud is perfused by a vascular plexus from the dorsal aorta which regresses with the development of the main pulmonary artery. Systemic supply to normal lung occurs due to failure of regression of the primitive aortic branches to the developing lung bud [5]. The basal segments of the lower lobes are commonly affected with a slightly higher incidence noted in the left lower lobe. The systemic supply usually arises from the thoracic aorta but can arise from the suprarenal abdominal aorta or the coeliac axis and in rare instances, from the left subclavian or internal mammary artery [6]. The venous drainage is usually through the inferior pulmonary vein into the left atrium.

Transmission of the systemic pressure to the low-pressure pulmonary vasculature results in a focal pulmonary hypertension which in severe cases can develop into high-output cardiac failure. The most common presenting symptom is hemoptysis. Other manifestations include exertional dyspnea, congestive heart failure due to left heart overload.

Chest radiographs may show ill-defined opacity corresponding to the anomalous artery. CT angiography can demonstrate the origin and course of aberrant artery with the advantage of multiplanar and 3-D reconstructions. CT helps in excluding other causes of systemic arterialization of lung like bronchopulmonary sequestration and other pulmonary vascular anomalies like congenital pulmonary venolobar syndrome. Intralobar sequestration appears as an area of consolidation or rarely as a cystic lesion with systemic arterial supply and normal pulmonary venous drainage but without any visible communication with tracheobronchial tree. Conventional angiography has been superseded by CT angiography but remains an important problem-solving tool and plays a vital role in the endovascular management of these patients. Treatment options include surgery (lobectomy and segmentectomy), when aberrant systemic artery is the only supply, and occlusion of the aberrant vessel by surgical ligation or endovascular treatment (embolization) when the involved segment has dual blood supply [7].

Teaching point

Anomalous arterial supply to lung is an important differential diagnosis to consider in imaging of haemoptysis and should actively searched for in cases where no attributable causes are identified on first look.

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