A new intracavitary lesion at echocardiography and MR: a case of mistaken identity.

Atrial myxomas often show contrast enhancement following administration of intravenous gadolinium, whereas thrombus appears as a hypointense structure, typically without any contrast enhancement. This case report presents a diagnostic challenge involving a recently developed left atrial mass in which echocardiography and cardiac MRI provided discordant results. While the morphological characteristics of the new left atrial lesion were suggestive of myxoma, the signal characteristics and behavior following intravenous gadolinium at MR, and, in particular, the rapid interval appearance of the lesion, prompted consideration for left atrial thrombus. Subsequent intra-operative and histopathologic evaluation proved the mass to be a left atrial myxoma.