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Findings: A single PA view of the chest demonstrates pleural calcifications along the costal margins bilaterally within the mid lung zones. In addition, linear calcification is also seen overlying the left hemidiaphragm. There is a 4 cm. mass-like opacity at the right lung base.
CT examination to the chest was performed at 8 mm. sections and filmed at lung and mediastinal windows, with 2 mm. thin sections at the right lung base.
Multiple calcified pleural plaques are noted bilaterally with associated bilateral pleural thickening. There is a 2.5 x 2.5 cm. mass along the posterior surface of the right lower lobe which contains a few linear and stippled calcifications in its anterior aspect. Bronchovascular bundles within the vicinity of the mass appears to converge on this region.
Impression: Radiographic findings suggestive of asbestos exposure. In addition, a 2.5 cm. soft tissue mass at the right base associated with pleural thickening. The differential includes rounded atelectasis versus malignancy.
Diagnosis: Rounded atelectasis in a patient with prior asbestos exposure.
Discussion: Fraser and Parč described rounded atelectasis as an unusual manifestation of passive atelectasis. It was originally described by Loeschke in 1928 and discussed in 1966 by Blesovsky who called it (the folded lung). It has also been described as shrinking pleuritis without atelectasis, pleural fibroma, pseudotumor, and vanishing lung.
Radiographically it is identified as a round peripheral parenchymal lesion adjacent to an area of pleural thickening. The margins may be sharply or poorly defined. Curvilinear bronchovascular bundles are seen to converge or be drawn inward toward this lesion. In addition they can be described as radiating from the lesion towards the hilum. As described by Menzies there are two theories as to the pathogenesis of rounded atelectasis. The initial theory proposed by Loeschke is believed to be caused by a pleural effusion which is large enough to cause a portion of the lung to float and separate from the parietal pleura which then results in a focal area of collapse, presumably due to compression. An alternative explanation was proposed by Blesovsky who believed it to be secondary to an injury to the pleura that leads to an inflammatory reaction and associated fibrosis. As the fibrous tissue matures it contracts pulling the underlying pleura with it. The pleura is compressed resulting in buckling into the lung like an accordion. This buckling then is believed to lead to collapse of lung parenchyma.
This case demonstrates converging bronchovascular bundles and associated mass in an area of pleural thickening. In the two series described by McHugh and Menzies, most of the individuals in their studies had a history of asbestos exposure. In the study by McHugh, they described three CT criteria which may lead to the diagnosis of rounded atelectasis; 1) a rounded or oval mass measuring approximately 3.5 x 7 cm. in diameter which abuts a pleural surface in the lung periphery, 2) vessels and bronchi curving into the mass and blurring the central margin, and 3) associated pleural thickening with or without calcification. When these criteria are met, further diagnostic evaluation is unnecessary. However, because rounded atelectasis and bronchogenic carcinoma have certain pathogenic factors in common and can rarely coexist, if there is any doubt about the radiologic criteria, percutaneous needle biopsy is believed to be a prudent precautionary measure.
References:
1. McHugh K and Blaquiere RM: CT Features of Rounded Atelectasis.
American Journal of Roentgenology 153:257-260, 1989.
2. Menzies R, and Fraser R: Round Atelectasis Pathologic and Pathogenetic Features.
American Journal of Surgical Pathology. 11:674-681, 1987.
3. Fraser RS: In Synopsis of Diseases of the Chest, 2nd Edition, Philadelphia, W. B. Sanders, 1994.
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