Teaching Case

A 60-year-old man with cough and fever underwent chest radiograph.
In the lateral projection a parenchymal opacity in the left lower lobe was noted. In the posteronterior projection the lesion did not silhouette the heart or the diaphragm (Fig. 1). A CT study was ordered for further investigation.

As a congenital anomaly was suspected it was decided to perform a CT angiography according to standard protocols and arterial, venous and delayed phases were obtained in order to assess its vasculature. Maximum Intensity Projections (MIP) reconstructions in orthogonal views were also obtained.
At the postero-basal segment of left lower lobe level, CT revealed an area of parenchymal consolidation with smooth borders, serpiginous morphology, without air bronchogram (Fig. 2). An abnormal arterial branch originating from the descending thoracic aorta was also seen (Fig. 3, 4 and 5).
The aberrant pulmonary parenchyma was drained from the pulmonary veins (Fig. 6).
A surrounding area of hypodensity mimicking "emphysema" (Fig. 7) was also disclosed.

Sequestration consists of an area of disorganised pulmonary parenchyma without normal pulmonary arterial vasculature or bronchial communications.
Two types of sequestration are described: the intralobar (most common) and the extralobar one [1].
Most of the cases of pulmonary sequestration diagnosed in the adult are intralobar, therefore they are contained in the lung parenchyma (in 65% of cases at the left lower lobe) and they are not covered by the visceral pleura. In most cases, these are an acquired disease, secondary to chronic infections which lead to the destruction of the normal pulmonary arterial supply and subsequent systemic arterial neovasculature. Usually the pulmonary drainage occurs through the pulmonary veins, more rarely through the azygos or hemiazygos system. Sequestration may appear as a homogeneous mass or as a well-defined cystic or multicystic lesion filled with air and fluid.
The extralobar sequestration is a congenital form, almost always observed in neonates and infants, leading to an abnormal budding of the primitive cephalic portion of the intestine. This lesion is equipped with its own visceral pleural lining, is situated in 90% cases at the base of the medial left lower lobe, is almost always free of air and of connections with the pulmonary artery or normal bronchial afference. The arterial supply originates from the abdominal aorta or the lower portion of the thoracic aorta, while the venous drainage may be supported by the inferior vena cava, the azygous vein or the portal vein [2].
The association with other congenital anomalies is common, particularly with anomalies of the diaphragm and hypoplasia of the ipsilateral lung [3].
The therapy consists in surgical excision (segmental resection or lobectomy) and it may present difficulties depending on the characteristics of the abnormal vasculature.