Round atelectasis.

Round atelectasis is a little-known form of peripheral pulmonary collapse which may mimic a neoplastic tumor. Usually the atelectasis forms a well-demarcated round or oval intrapulmonary pleural-based mass at the basal, posterior or interlobar pleura. It is thought to be a sequela of a pleural effusion. If the radiographic features are characteristic, and fine-needle biopsy finding negative, the diagnosis of round atelectasis can be made with assurance, and unnecessary procedures such as thoracotomy and pulmonary resection can be avoided. In this paper experiences of 11 patients with this condition are presented. In 4 the diagnosis was established by surgery and in 7 a long-term follow-up confirmed the diagnosis of a nonmalignant intrapulmonary lesion. The pathogenesis, clinical and radiological features, and the diagnostic workup are discussed.