Defying gravity: subdiaphragmatic causes of pleural effusions.

Intra-abdominal fluid may migrate readily into the pleural space through naturally occurring holes in the diaphragm or intradiaphragmatic lymphatics. Although any type of fluid in the abdomen may migrate, additional pathologic mechanisms are involved in the development of chylous ascites/chylothorax, yellow nail syndrome, urinothorax, pancreaticopleural fistulas, or other connections. In the differential diagnosis of the large list of potential pleural fluid causes, intra-abdominal sources should be entertained by the practicing physician in the right clinical context.