[The magnetic resonance characteristics of rounded atelectasis]

Rounded atelectasis is a peculiar form of lung collapse which is well known by radiologists. Its appearance on conventional radiographs and CT is by now well recognized and widely reported. Even though these two techniques usually allow a diagnosis to be made, the MR appearance of rounded atelectasis is worth mentioning as well. This diagnostic imaging technique is widely employed, and our experience suggests that, in some cases, MR Imaging can give an important contribution to the study of this condition. We report our experience with 6 cases of rounded atelectasis in 5 patients (one patient had bilateral lesions). Five signs characteristic of rounded atelectasis were observed: some of them are seen on both conventional radiographs and CT scans, others are typical of the latter technique. All cases showed peripheral location of the lesions and the "comet tail" sign--i.e., vascular structures gently curving into the mass. These two signs are also observed on conventional radiographs and CT scans. Typical of MR imaging are the extant 3 signs: low signal in T1 and high signal in T2-weighted images in the whole of our cases; no signal from pleural thickening next to the mass in T2-weighted images, and, finally, the "kidney-like" pattern--i.e., hypointense lines converging toward the center of the mass. All these signs, which were always observed in our series, support the current etiopathogenetic hypothesis of pleural effusion as an early sign, which is reported to be followed by fibrous pleural involution which wraps atelectatic parenchyma up. On the basis of these typical MR features a correct diagnosis can usually be made even in those cases in which conventional radiography and CT do not allow a definite diagnosis.