Which finding is shown in this image?

The echocardiographic image shows a mobile, highly echogenic, mesh-like structure within the right atrium consistent with the Chiari network. The Chiari network is an embryologic remnant of the right valve of the sinus venosus, appearing as a fenestrated, reticulated membrane that is usually thin and mobile, found near the orifice of the inferior vena cava or the coronary sinus.

This structure is benign and often an incidental finding but can be confused with thrombus or atrial tumors. Unlike left atrial thrombus, which appears as a more solid, immobile mass often located in the left atrial appendage, the Chiari network is mobile and located in the right atrium. Cor triatriatum is a rare congenital membrane dividing the left atrium into two chambers and appears differently on echocardiography. Artifact refers to non-anatomic echoes which do not persist or move consistently.

Recognition of Chiari network is important to avoid misdiagnosis, and its characteristics are well described in echocardiography literature such as the "Textbook of Clinical Echocardiography" and ASE imaging guidelines【16:Textbook of Clinical Echocardiography, 6e†p.400-402】【12:ASE Guidelines on Cardiac Masses†p.150-155】.