Mediastinal teratoma masquerading as idiopathic enlargement of the right atrium

A chest roentgenogram of an asymptomatic 22-year-old man revealed prominence of the right heart border characteristic of idiopathic dilatation of the right atrium. On further evaluation, a malignant teratoma was found. The importance of including teratoma and idiopathic enlargement of the right atrium in the differential diagnosis of abnormalities of the right heart border is discussed.