M-mode ultrasonic localization and identification of fluid-containing pulmonary cysts

Successful ultrasonic localization of pleural fluid has been well documented in recent reports. The ability of ultrasound to detect and identify fluid within a parenchymal lesion has not been defined. We examined nine patients with cystic lesions and air-fluid levels noted on the chest roentgenogram. In all nine patients, an echo-free space that corresponded anatomically to the level of fluid noted on the x-ray film could be recorded in the M-mode presentation. The combined thickness of the wall of the chest and the overlying lung as judged by ultrasound ranged from 2 to 8 cm, with a mean of 4 cm. The following two characteristics appeared to distinguish parenchymal from pleural fluid: (1) similar characteristics of motion of the proximal and distal interfaces of the sonolucent space; or (2) the ultrasonographic pattern of overlying lung proximal to the loculation of fluid. Ultrasonograms in eight (89 percent) of nine patients demonstrated one or both of these characteristics. These findings indicate that ultrasound can detect fluid within a parenchymal structure and may be used to differentiate intraparenchymal loculations from those in the pleural space.