Teaching Case

A 76-year-old man with history of asbestos exposure presented to the emergency department for chest pain, cough and dyspnoea.

The chest radiograph showed a well-defined oval mass in the right lower lobe, which was most possibly pleurally based with associated volume loss and presence of bilateral pleural effusions (Fig. 1).
CT of the chest demonstrated a pleurally based well-defined round mass in the right lower lobe, with air bronchogram centrally, associated with distortion, displacement and convergence of adjacent broncovascular structures and volume loss (Fig. 2). Small calcified pleural plaques, pleural thickening and pleural effusion were also observed (Fig. 3, 4). The mass enhanced homogeneously after contrast administration (Fig. 3, 4). No filling defects were detected in the main lobar or segmental branches of the pulmonary arteries (Fig. 3b).

Rounded atelectasis is a benign condition in which a peripheral lung area collapses and is surrounded by pleural invagination. This form of atelectasis has also been termed ‘folded lung’, ‘pseudotumour’, ‘pleuroma’, ‘Blesovsky syndrome’, ‘pleural asbestotic pseudotumour’ and ‘twisted lingula’ [1, 2].
Rounded atelectasis can result from any type of pleural inflammatory reaction, with asbestos being the most common cause [1]. The pathogenesis is not clear, but it probably represents an inflammatory reaction of the pleural surface with development of fibrosis tissue [2, 3, 4]. As this fibrous tissue matures, it contracts with the lung causing pleural invagination and parenchymal collapse [2-4].
Rounded atelectasis is usually asymptomatic [1], with chest pain and cough generally being the most common symptoms either due to the pleuritis or due to the underlying disease [3].
Chest radiography shows a round or oval well-defined mass, demonstrating the "incomplete border sign" representing a pleurally-based mass. There is associated volume loss and obliteration of the costophrenic angle due to pleural thickening [1].
CT shows a round or oval well-defined mass that has a broad contact with the pleura and is associated with distortion, displacement and convergence of adjacent bronchovascular structures (“vacuum cleaner effect” or “comet tail” sign) [1-5]. Volume loss of the affected lobe is frequent, but not constant. Rounded atelectasis is often associated with other asbestos exposure findings such as pleural plaques, pleural thickening or pleural effusion [1-5]. However, the absence of these findings does not exclude asbestos exposure as the cause of this entity [2]. After contrast administration rounded atelectasis enhances homogeneously, although this finding is not useful to differentiate it from bronchogenic carcinoma [3].
MRI often shows a mass with low signal intensity on T1 weighted-sequences with distortion and convergence of adjacent bronchovascular structures that manifest as curved low-signal-intensity lines due to visceral pleura thickening.
Rounded atelectasis often remains stable on long-term follow-up, although it may decrease or disappear completely. Enlargement has been reported in very few cases [3].
Radiologic follow-up is recommended. Fine needle aspiration is reserved just for atypical cases and excisional biopsy is rarely performed [3-5].