Ultrasonographic forms of pleural space in healthy children

This prospective study was conducted to detect physiological pleural fluid using chest ultrasonography in healthy children, to assess frequency of this finding, to check the general status of pleural space and to describe possible individual variations of the amount of pleural fluid present in healthy children. Chest ultrasonography of both pleural spaces was performed in a group of 100 randomly selected healthy children, searching for pleural fluid. Children were examined in the elbow position after leaning five minutes in lateral decubitus position. Ultrasonographic images were acquired with a 3-12 MHz linear transducer. The presence of the fluid was assessed and measured as an anechoic layer exceeding at least 2 mm in thickness. The study was repeated on each subject after a time interval of one to two months. Fluid was quantified and compared intraindividually using student t-test. Presence of pleural fluid was found in 35/100 healthy children (35%) in both the baseline study and the follow-up study. Only two children had different results at follow up. In case of a positive finding, the fluid was found in both, left and right pleural space in fourteen out of 35 children (40%). In the remaining 21 out of 35 (60%) children fluid was detected only in one pleural space. Thickness of the pleural fluid ranged from 2 mm to 3.4 mm (mean 2.4 +/- 0.3 mm) in the baseline group and from 2 mm to 3.7 mm (mean 2.5 +/- 0.4 mm) in the follow-up group. Overall pleural fluid was observed in 36 subjects with high reproducibility of 94% after delay of 1-2 month as 34 of them presented pleural fluid twice. Chest ultrasonography allows detecting small collections of pleural fluid in healthy children. The results of our study prove that the amount of physiologic pleural fluid is a stable individual characteristic of a healthy child. Such a positive result (less than 4 mm in the elbow position), if isolated, should be taken as normal finding, and requires no additional investigation.