Pulmonary sequestration. Visualization of an enlarged azygos system by CT.

The purpose of this study was to determine the prevalence of enlargement of the azygos system in the case of lung sequestration and its potential usefulness in the differential diagnosis of lower lobe opacities. Seven consecutive adult cases of pulmonary sequestrations were retrospectively enrolled; 4 sequestrations were proved surgically and all 7 angiographically. A group of 50 consecutive patients with a normal chest CT were used as controls. Another group consisted of 25 consecutive patients identified on the basis of an opacity in a posterobasal location on chest CT. For the 3 groups, the maximum diameter of the azygos and hemiazygos veins was measured, the level of measurement located between the upper poles of the kidneys and the confluence of inferior pulmonary veins into the left atrium. The diameter of the azygos veins (mean 10.4 +/- 5.1 mm) and of the hemiazygos veins (mean 7.1 +/- 3.0 mm) in the sequestration group was significantly larger than the diameter of the azygos and hemiazygos veins in the control group (mean 5.7 +/- 2.5 mm, and 3.4 +/- 2.4 mm, respectively), as well as in the study group (mean 5.9 +/- 2.6 mm and 3.3 +/- 2.6 mm, respectively). Our results suggest that enlargement of the azygos system in association with a posterobasal chest opacity, although nonspecific, may be a useful additional CT sign of sequestration.