Cardiac involvement in hypereosinophilic syndrome

A 9-year-old boy with hypereosinophilic syndrome (HES) was referred for cardiac magnetic resonance (CMR) imaging following an abnormal echocardiogram that showed a large mass layered on the inferolateral wall of the left ventricle, causing secondary severe mitral regurgitation. Cardiac involvement in HES usually affects the ventricular apex. In our case, CMR confirmed the presence of a large mural thrombus of 0.9 cm × 4.2 cm. This unusual cardiac involvement in HES was diagnosed in its intermediate thrombotic stage. CMR is very sensitive and specific in staging the disease. It explained the etiology of mitral regurgitation and guided therapy, especially when echocardiography was nonconclusive.