Intra-atrial extension of Wilms' tumor.

Echocardiography in a 4-year-old boy, with nephroblastoma of the left kidney, revealed a large homogenous mass in right atrium extending from inferior vena cava, and protruding through tricuspid valve into right ventricle during diastole. Ultrasonography revealed the contiguous spread of the tumor through renal vein with near total caval occlusion. The patient had a fatal outcome before definite treatment could be started. Intracardiac extension of infradiaphragmatic tumors through caval route, although infrequent, can be seen with renal cell carcinoma, Wilms' tumor, hepatoma, lymphoma, and uterine and adrenal tumors. Detection of a mass in right atrium in a child should alert the echocardiographer about the possibility of caval spread from a renal neoplasm.