Background: The pleural line in lung ultrasound normally appears as a single, thin, hyper echoic contour representing the close adherence of the parietal and visceral pleura. Under certain chronic or post-inflammatory
conditions, these layers may be visualized separately.

Objective: To describe and interpret the pleural separation sign as a potential sonographic indicator of chronic visceral pleuritis.

Methods and Observations: In basal and posterior lung zones, 2.5-5MHz frequency ultrasound probe revealed double pleural contours in chronic pulmonary and post-cicatricial disease. This likely reflects fibrotic or ischemic remodeling of the visceral pleura leading to partial decoupling from the parietal layer.

Conclusion: The pleural separation sign may assist in differentiating chronic from acute pleural processes and even chronic from acute pulmonary embolism, particularly in posterior–basal regions where mechanical and vascular factors favor stable visualization.

Keywords: pleural separation sign; chronic visceral pleuritis; lung ultrasound; posterior–basal predominance;
pulmonary embolism.