Two dimensional echocardiographic recognition of the descending thoracic aorta: value in differentiating pericardial from pleural effusions.

The course of the descending thoracic aorta has recently been visualized with two dimensional echocardiography and its presence confirmed with contrast studies. In the parasternal short axis view, we used the location of the descending thoracic aorta to differentiate pericardial from pleural effusions in 40 patients. Sixteen patients, each with an isolated pericardial effusion, had an echo-free space between the descending thoracic aorta and left ventricular posterior wall. Nine patients, each with an isolated pleural effusion, had an echo-free space posterior to the descending aorta. Fifteen patients, each with both a pericardial and pleural effusion, had echo-free spaces both between the descending thoracic aorta and left ventricular posterior wall and also posterior to the descending thoracic aorta. With one exception, all patients had anatomic confirmation of these findings. Forty-one patients undergoing cardiac surgery served as controls and none had a posterior echo-free space in relation to the descending thoracic aorta. At operation, no pericardial or pleural effusion was evident. The location of the descending thoracic aorta on two dimensional echocardiography serves as a valuable landmark in localizing the pericardial-pleural interface, thereby differentiating pericardial from pleural effusions.