Teaching Case

A 45-year-old man presented with shortness of breath and chest pain. A CT Pulmonary Angiogram (CT PA) was ordered for investigation of a pulmonary embolus.

The CT PA showed a hypodense area in the posterobasal segment of the left lower lobe. This area appears to mimic a bullous lesion in emphysema, however, with vessels extending from it (Fig. 1).

An abnormal arterial branch originating from the descending thoracic aorta was also evident (Fig. 2). The venous drainage was not appreciable in any of the images. It was not possible to differentiate whether the lesion was intralobar or extralobar.

Pulmonary sequestration is a segment of non-functioning lung parenchyma which has no connection to the tracheobronchial tree and receives its blood supply from an aberrant systemic artery. Thus, there is no ventilation /perfusion in the sequestrated segment [1, 3].

Traditionally, pulmonary sequestrations are divided into intralobar sequestrations (ILS) and extralobar sequestrations (ELS). The two types of sequestrations are similar in their relationship to the bronchial tree and arterial supply but differ in their venous drainage system [2, 4].

Pulmonary sequestrations are rare, accounting for approximately 0.15-6.4% of all congenital pulmonary malformations [1, 2, 5].

ILS account for approximately 75-85% of all sequestrations and are characterized by development within the visceral pleura, an aberrant systemic artery (usually a branch of the aorta) and venous drainage by the pulmonary veins but can occur through the azygous / hemiazygous vein, portal vein or IVC [3, 5]. ILS usually present in older age with recurrent infections. Infections can occur due to anomalous connections with bronchi, lung parenchyma or the GIT, which can allow bacteria to enter the sequestration [1, 2, 4].

ELS account for approximately 15-25% of all sequestrations and are characterized by a separate pleural segment without any lung parenchyma, a small aberrant systemic artery and drainage through the systemic veins or directly in the right atrium [2, 5, 6]. ELS usually present in the neonatal period and can be supradiaphragmatic (90%) or infra-diaphragmatic (10%) [5, 6].

On prenatal diagnosis, pulmonary sequestrations are diagnosed on ultrasound as echo dense homogeneous masses. MRI is the best tool in diagnosis of sequestrations and for differential diagnosis amongst other entities, such as congenital diaphragmatic hernia and congenital pulmonary airway malformations [5].

Postnatal diagnosis of pulmonary sequestrations is initially shown on chest radiographs and clarified best by contrast enhanced helical CT. MRI is particularly helpful in delineating complex lesions and congenital diaphragmatic hernias. Ultrasound may also be very useful in accurate and prompt diagnosis during the neonatal period [6, 7].

Surgical treatment is conventionally divided into symptomatic and asymptomatic patients. Treatment is considered only for those who are symptomatic such as neonates with ARDS or can be elective for older patients with recurrent infections [8].

Video-assisted thoracoscopic surgery (VATS) can be used to resect pulmonary sequestrations as long as accurate delineation of the aberrant blood supply can be achieved [8]. 3D CT and MRI are often used prior to surgery to map out the lesion and its blood supply [7, 8].