Chest CT scan from a 70-year-old man with no known cigarette or asbestos exposure shows a 2-cm rounded mass in the periphery of the left lower lobe that forms an acute angle with the pleura, contains an air bronchogram at its central ill-defined margin, and is not completely surrounded by lung (A). Also seen is a curvilinear opacity that converges into the mass at its inferior pole (B). Pleural thickening with calcification is seen adjacent to the mass (A and B).
The left lower lobe mass showed no evidence of malignancy on transthoracic needle aspiration (TTNA) and showed no uptake on FDG scanning. There has been no change in size of the mass in 1 year.
Rounded atelectasis represents an unusual form of lung collapse that occurs usually adjacent to scarred pleura and can be mistaken for lung cancer. It has been referred to as folded lung, Blesovsky syndrome, atelectatic pseudotumor, and shrinking pleuritis with atelectasis (1).
Pathologically rounded atelectasis consists of a focus of collapsed lung parenchyma partly surrounded by thickened invaginated pleura, that is approximately 5 mm thick and extends several centimeters into the adjacent lung. Pleural wrinkling and folding and a variable degree of alveolar collapse and fibrosis is seen on microscopic examination. These findings form the basis for the explanation that most cases are related to pleuritis and pleural fibrosis leading to contraction of the pleura and its’ subsequent invagination into contiguous lung causing parenchymal compression (1). An alternate explanation suggests that in an area of pleural effusion, regional lung becomes adherent to the parietal pleura and interlobar fissure. As the fluid resolves the more central lung expands leaving the peripheral lung adherent to the pleura, atelectatic and rolled into a round configuration (1).
Radiographic and CT scan features of rounded atelectasis are characteristic enough to be diagnostic so that in most cases it need not be mistaken for lung cancer (2). These include a rounded peripheral lung mass, most dense at its periphery, that is not completely surrounded by lung. The mass forms an acute angle with the pleura and its central margin is blurred. Adjacent pleural thickening is always seen and an air bronchogram is usually present in the proximal or central part of the density. One of the most helpful diagnostic signs is the demonstration on chest CT of a peripheral lung mass with an ill defined central margin toward which traverse bronchovascular bundles in a curvilinear fashion resembling a comet tail (3). The ‘comet tail’ sign is not always evident on conventional CT because of the oblique and cephalocaudal orientation of bronchi and vessels. In such situations, spiral CT with multiplanar reconstruction or MRI may be more revealing (4).
Most patients with rounded atelectasis have a history of asbestos exposure. However, tuberculosis, pulmonary infarction, postpericardiotomy syndrome, malignancy, and cardiac failure have all been implicated in its formation (4).
When the characteristic imaging findings are present, the diagnosis is rarely in doubt and further investigation is not necessary (2). FDG PET scanning, MRI, TTNA, radiographic follow up for increase in size, or lung resection are options when the diagnosis is in doubt.
1. Partap VA. The comet tail sign. Radiology. 1999; 213: 553–554.
2. Doyle TC, Lawler, GA. CT features of rounded atelectasis of the lung. AJR Am J Roentgenol. 1984; 143: 225–228.
3. Carvalho PM, Carr D. Computed tomography of folded lung. Clin Radiol. 1990; 41: 86–91.
4. Fraser RS, Müller NL, Colman N, et al. Atelectasis. In Fraser & Pare’s Diagnosis of Disease of the Chest, vol 1. Philadelphia: Saunders; 1999: 521–522.