[Extra echo spaces: what do they represent?].

The echocardiographic diagnosis of pericardial effusion is based on the assumption that "echo-free spaces" observed behind the posterior wall of the left ventricle are surrounded by epicardium and pericardial echoes. However, inexplicable extra echo spaces (EES) which may either be echo-dense or echo-free are observed in many asymptomatic patients. These EES often show no changes in their sizes or contours during lengthy follow-up studies. Therefore, we propose a hypothesis that subepicardial fat rather than effusions may be the cause of such EES. According to this hypothesis, a border zone of myocardium and subepicardial fat produces a linear echo which has been misinterpreted as an epicardial echo. Furthermore, a dense, broad band-like echo behind the posterior wall of the left ventricle believed to be a pericardial echo is a fusion echo caused by epicardium, pericardium and pleura. Differentiating EES as due either to subepicardial fat or pericardial effusion is difficult echocardiographically; however, CT scans can differentiate them due to their differing CT values. The echocardiographic diagnosis of pericardial effusion is more easily made among young patients who do not have appreciable subepicardial fat, or massive pericardial effusions causing pendulum-like movements of the heart.