Objective: Cardiac septal aneurysms in adults are diagnosed when the interatrial or interventricular septal membrane deviates more than 10-15 mm to either side in the cardiac chamber. Routine non-ECG-gated chest CT does not have sufficient temporal and spatial resolution for adequate characterization of such an entity. We report the imaging findings of cardiac septal aneurysms depicted in two patients with ECG-gated cardiac MRI and in a third with ECG-gated cardiac 64-MDCT. Each aneurysm was initially believed to be a cardiac tumor on the basis of the appearance on non-ECG-gated chest CT or MRI.
Conclusion: Nonopacified blood can fill a cardiac septal aneurysm and mimic a pseudomass. It is important that radiologists recognize such an entity on chest CT and MRI because of the association with intracardiac shunting and stroke and to avoid misdiagnosis of an aneurysm as a cardiac tumor.