The causes of thrombosis at the site of rounded atelectasis

been described in the hiterature,’ this is the first case in which this usually innocuous pleural mass has produced significant morbidity and contributed to a patient’s death. The special features ofthis case include the demonstration of local extrinsic compression of the airway seen on bronchoscopy, postobstructive pneumonia in the occluded segments, and local pulmonary artery thrombosis in the affected lobe. Development of obstructive pneumonia in rounded atelectasis is understandable. The mass, composed of intertwined thickened pleura and atelectatic lung, can entrap and extrinsically compress neighboring bronchi. With ohstruction comes a breakdown of local antibacterial mechanisms and the development of infection in the airway. In a report by Hillerdal,’ two patients with rounded atelectasis died of pneumonia, but the relationship to rounded atelectasis was not mentioned. It is possible that this patient’s age and prostatic carcinoma may have increased his susceptibility to infection as well, even though his white blood cell count was normal. The causes of thrombosis at the site of rounded atelectasis are possibly twofold. First, with kinking of blood vessels secondary to rounded atelectasis, regional blood flow may decrease and the concentration of procoagulants in local vessels may rise high enough to initiate clotting. Second, damage ofthe blood vessel caused by kinking and distortion may induce the formation of prothrombin activators which initiate the cascade leading to clot formation.#{176}It is possible to see pulmonary vascular thrombosis in association with severe pneumonia. However, the presence of thrombosis only in the atelectatic lobe in this patient makes local alterations related to the pleural mass the more likely cause. Another interesting facet ofthis case is the notable absence of any radiographic evidence of small pneumoconiotic opacities, despite the severe parenchymal involvement with asbestosis found at autopsy. The dissociation between the chest radiograph and histology in asbestosis is well descrihed. Epler et al have shown that approximately 10 percent of individuals with chronic diffuse infiltrative lung disease have normal chest roentgenograms. That series included six cases of radiographically inapparent asbestosis. Rockoffand Schwartz have estimated that application of the International Labour Organization classffication can result in a 10 to 20 percent probability of a normal radiograph interpretation in cases ofhistologically significant asbestosis. Several articles have described the chest radiographic, bronchographic, tomographic and CT appearance of rounded atelectasis.’#{176} ’ In most cases, the plain film shows a rounded mass within the lower lobe, as was found in this patient. Lateral tomography may show vessels and bronchi near the mass curving toward and converging on the edge of the mass. The CT scan may show a rounded mass, 4 to 7 cm in diameter, most dense at its periphery, which forms an acute angle with the pleura, with pleural scarring thickest adjacent to the mass. Vessels and bronchi may be seen curving toward the mass. Recognition of these features, while not strictly pathognomonic,’ can generally forestall invasive testing and surgical intervention.” However, even though rounded atelectasis is generally benign and sometimes associated with spontaneous resolution,111216 this case demonstrates how it can secondarily contribute to patient morbidity and mortality.