Magnetic resonance imaging of rounded atelectasis.

This study describes the magnetic resonance imaging (MRI) findings of rounded atelectasis (RA) and compares them with computed tomography (CT) findings. The study sample comprised 15 cases of RA in which both MRI and CT were performed. The signal intensity of RA was higher than that of muscle and lower than that of fat on T1-weighted images, and similar to or lower than that of fat on T2-weighted images. The atelectatic mass homogeneously enhanced after gadopentetate dimeglumine administration. Structures within and surrounding the RA were clearly depicted on MRI. The pulmonary vessels and bronchi converging toward the area of atelectasis (comet tail sign) were better demonstrated by sagittal or oblique sagittal MRI in six cases. RA and thickened pleurae were more clearly separated on T2-weighted images compared with CT. An infolded visceral pleura was demonstrated as a low-signal-intensity line in seven cases, and a small amount of entrapped pleural effusion was noted in one case. Although MRI should not be performed in all cases of suspected RA, it is useful, especially in delineating the internal structure of RA, such as the infolded visceral pleura.