Clinical History
Unsteady gait and vertigo. On clinical and laboratory examinations no abnormalities were found.
Imaging Findings
Patient admitted to the hospital because of unsteady gait and vertigo. On clinical and laboratory examinations no abnormalities were found. However, on routine chest radiograph, opacities were seen, which were consecutively evaluated by CT scan.
Discussion
Rounded atelectasis is an unusual form of peripheral lobar collapse, described in the literature under various names i.e. folded lung and atelectatic pseudotumor. The pathogenesis of rounded atelectasis remains controversial. Most authors believe that repeated pleural irritation from tobacco, asbestos and silica causes a localized visceral pleural fibrotic reaction. Subsequent pleural shrinkage causes folding and atelectasis of the underlying parenchyma with a rounded configuration. According to another theory, rounded atelectasis occurs secondary to compression of a peripheral portion of the lung by pleural effusion. The parenchyma collapses and becomes trapped within the effusion. When pleural effusion resolves, the atelectatic lung remains trapped and tends to roll into a ball.
The majority of patients with rounded atelectasis are clinically asymptomatic. Eighty percent of these lesions are localized in the posterior part of the lower lobes, mostly unilateral. Radiographic features of rounded atelectasis are characteristic and mostly diagnostic. Solitary atelectasis usually presents as a sharply marginated, rounded or oval pleural based mass, with a diameter of 4-7 cm. The mass forms an acute angle with the pleura, indicating its intrapulmonary location. Air bronchogram may be present while pleural thickening usually is most pronounced at the site of the mass. There is no or little radiographic evidence of volume loss, however a compensatory hyperinflation of the lung adjacent to the mass, thickened and/or displaced interlobar fissure, as well as limited pleural effusion are frequently observed.
The most characteristic feature is the so called "comet tail" sign, formed by the arcuate course of the pulmonary vessels and bronchi as they enter the atelectatic lung from above. Differential diagnosis should include mesothelioma and bronchogenic neoplasm. Frequent radiographic follow-up is needed to exclude malignancy. On the follow-up radiographs the lesion usually remains unchanged, but regression or even complete disappearance have also been reported.
Differential Diagnosis List
