Prolapsing Chiari malformation in tricuspid regurgitation: a moving filling defect in the inferior vena cava.

A membranous flap was observed during systole within the superior portion of the inferior cava in four patients who did not have either an indwelling catheter or a filtering device. In these cases, multiple views established that this line was not an artifact. Subcostal scans of the right atrium demonstrated a typical Chiari malformation. A diagnosis of tricuspid insufficiency was suspected because of the prolapsing Chiari malformation into the inferior vena cava, and confirmed by Doppler echocardiography. These cases expand the differential diagnosis of filling defects within the inferior vena cava, and emphasize the need for evaluating the right atrium as an extension of the cava, especially by sonographers who are not conversant with echocardiography.