From the Archives of the AFIP: Intralobar Sequestration

Radiologic-Pathologic Correlation

Abstract Introduction Postulated Pathogenesis Clinical Characteristics

Pathologic Features Histologic Features Radiologic Appearance

Therapy And Prognosis Conclusions Source Information References

Introduction

Pulmonary sequestrations are rare abnormalities that constitute 0.15% 6.4% of all congenital pulmonary malformations (1). A pulmonary sequestration is generally defined as nonfunctioning lung tissue that is not in normal continuity with the tracheobronchial tree and that derives its blood supply from systemic vessels (2). Pryce (3) first coined the term pulmonary sequestration in 1946 and further classified the lesion as intralobar or extralobar on the basis of the morphologic patterns of sequestration.

Intralobar sequestrations account for 75% of all pulmonary sequestrations. An intralobar sequestration consists of an abnormal segment of lung tissue that shares the visceral pleural covering of an otherwise normal pulmonary lobe and that lacks a normal communication to the tracheobronchial tree, although variable amounts of air may be contained within the anomalous tissue (Figure 1) (1,2). Intralobar sequestration occurs almost always within the lower lobe and slightly more often in the left lung than in the right lung (1). The chief pathologic features are chronic inflammation, cystic change, and fibrosis (2). On a cut specimen, a region of dense parenchyma frequently containing multiple cysts is seen (2). The anomalous aortic branches that supply the lesion are characteristically located within the inferior pulmonary ligament (1). The great majority of intralobar sequestrations are drained by normal pulmonary veins into the left atrium (4).

Extralobar sequestrations are a completely distinct entity and constitute 25% of all pulmonary sequestrations. The malformation is typically found during the patients' first days to weeks of life and, less frequently, in late infancy or early childhood. An extralobar sequestration consists of a discrete, accessory lobe of nonaerated lung tissue that is invested in its own pleural envelope (1,4,5). Although typically found in the posterior costodiaphragmatic sulcus between the lower lobe and hemidiaphragm (63% 77% of cases), the anomalous tissue may occur in the mediastinum, in the pericardium, and within or below the hemidiaphragm (4). Extralobar sequestration histologically resembles normal lung parenchyma, although all structures are dilated (6). A cut specimen of the lesion is typically firm, is homogeneous, and may contain cystic areas (6). If the anomalous tissue contains air, one can infer the persistence of a patent connection to the gastrointestinal tract. This unusual feature allows the sequestration to be classified as a "bronchopulmonary foregut malformation" (4,7,8). Extralobar sequestration is typically (80% of cases) supplied by an anomalous artery that arises directly from the thoracic or abdominal aorta (6). The venous drainage of extralobar sequestration is usually systemic (80% of cases) through the azygos and hemiazygos system or superior vena cava into the right atrium (4).

In this article, the radiologic manifestations of intralobar sequestration are illustrated and correlated with the underlying pathologic characteristics. Theories supporting an acquired origin for intralobar sequestration are also presented, as well as the clinical and histologic features of the lesion.

Abstract Introduction Postulated Pathogenesis Clinical Characteristics

Pathologic Features Histologic Features Radiologic Appearance

Therapy And Prognosis Conclusions Source Information References