Case of the Month

Figure 1. (A) LAT view. (B) PA view. (C) CT, pulmonary window. Coned down view at the level of the basal segments of the LLL. (A,B and C) Large gloved finger images are seen in the posterior and lateral basal segments of the LLL. A hyperlucent area partially surrounds the gloved finger images in (B). The hyperlucent area seen in (B) suggests emphysematous changes in (C). The radiological findings are very compatible with a congenital bronchocele secondary to bronchial atresia.

Figure 2. (A and B) PA view on inspiration and expiration respectively. The further increase in the radiolucency of the left base on expiration indicates the existence of air-trapping by the posterior and lateral basal segments of the LLL.

Figure 3. (A and B) 3D reconstructions of left base. Arterial blood supply to the area of the bronchocele (Asterisk) is via an artery arising from the abdominal aorta, above the celiac trunk (Arrow in A). Venous drainage is through the left inferior pulmonary vein (Arrows in B). The systemic arterial supply and pulmonary venous drainage are those of an Intralobar Sequestration.

Figure 4. (A) Pathological Specimen. Close-up. The large bronchocele filled with mucoid material correlates well with the 3D reconstruction in (B).

Figure 5. (A) CT, pulmonary window at the level of the basal segments of the LLL. Coned down view of left hemithorax. . The hyperlucent area partially surrounding the bronchocele suggests the presence of emphysematous changes (B) Pathological Specimen. Areas of centrilobular emphysema and distal bronchiolectasis are seen surrounding the bronchocele.

Pulmonary sequestration belongs to the group of congenital anomalies originating in the primitive foregut or its lung bud. It represents lung tissue separated from the remainder of the lung, lacking a normal connection with the bronchial tree, and supplied by a systemic artery. There are two types of sequestrations: (1) Intralobar and (2) Extralobar. Intralobar sequestrations account for 75% to 85% of pulmonary sequestrations.

1. INTRALOBAR SEQUESTRATION
Most patients are young adults of either sex. Associated anomalies are uncommon.

Intralobar sequestrations are virtually absent in infants. Intralobar sequestrations are thought to be acquired in most instances. A history of recurrent pulmonary infections is common.

Intralobar sequestrations usually occur in the lower lobes, slightly more often on the left. Radiographically they present as a dense mass with smooth borders, as a homogeneous consolidation with irregular margins, or as a persistent recurrent pneumonia. Cavitation may be present without infection. If complicated by infection, it may present as a cystic mass lesion.

Intralobar sequestrations share the visceral pleura with the adjacent pulmonary lobe. They may be separated from the normal lung by a fibrous capsule, or by an indistinct transitional zone.

Pathologically they are made up of mucus/pus filled cystic spaces with intervening fibrotic lung parenchyma or areas of obstructive pneumonitis. Their arterial supply is systemic.

95% of the venous drainage of intralobar sequestrations is via the pulmonary veins. The venous drainage of the remaining 5% of patients is systemic.

2. EXTRALOBAR SEQUESTRATION

It is thought to develop from an anomalous/supernumerary lung bud that derives its blood supply from the primitive splanchnic vessels surrounding the foregut. These vessels, which are connected to the primitive dorsal aorta, form the anomalous arterial blood supply to the sequestration.

Extralobar sequestrations are more common in males (4:1). They are usually diagnosed in the prenatal or neonatal period, and are associated with other congenital anomalies, the most frequent being a congenital diaphragmatic hernia. Extralobar sequestrations in children and young adults are uncommon.

Radiographically they usually present as a well defined homogeneous triangular shaped mass lesions in the left posterior costophrenic angle between the lower lobe and the hemidiaphragm. They may present in the mediastinal region, within the pericardium or within or below the hemidiaphragm.

Extralobar sequestrations are enveloped in their own pleura. Airways are sparse, and the pulmonary parenchyma may be immature.

Arterial supply to extralobar sequestrations is systemic. In 5% of cases, the lesion is supplied by branches of the pulmonary artery or by both the pulmonary and systemic circulations.

Venous drainage is systemic in 80% of cases. An extralobar sequestration supplied by pulmonary arteries is more likely to have a pulmonary venous drainage.

Intralobar Sequestration:
Radiographically they present as a dense mass with smooth borders, as a homogeneous consolidation with irregular margins, or as a persistent recurrent pneumonia. Cavitation may be present without infection. If complicated by infection, it may present as a cystic mass lesion.

Extralobar Sequestration:
Radiographically they usually present as a well defined homogeneous triangular shaped mass lesions in the left posterior costophrenic angle between the lower lobe and the hemidiaphragm. They may present in the mediastinal region, within the pericardium or within or below the hemidiaphragm.

1. Rosado-de-Christenson ML, Frazier AA, Stocker JT, Templeton PA. Extralobar sequestration: radiologic-pathologic correlation. Radiographics 1993;13:425-441.
2. Frazier AA, Rosado de Christenson ML, Stocker JT, et al. Intralobar sequestration: radiologic-pathologic correlation. Radiographics 1997;17:725-745
3. Müller NL, Fraser RS, Soo Lee K, Johkoh T. Diseases of the Lung:   Radiologic and Pathologic Correlations. Philadelphia, PA: Lippincott Williams & Wilkins, 2003
4. Berrocal T, Madrid C, Novo S, et al. Congenital anomalies of the tracheobronchial tree, lung, and mediastinum: embryology, radiology, and pathology. Radiographics. 2003;24:e17