Abnormal pleura morphology Pleural cyst 2017-04-23T12:33:15Z Pleuropericardial cysts usually are congenital anomalies. after the third week of gestation, the mesoderm separates itself to form pleural, pericardial and peritoneal spaces. Incomplete partitioning can result in a pleuropericardial cyst. A closed sac-like structure originating from the pleura that contains a liquid, gaseous, or semisolid substance.