An edge shadow, also called an edge artifact or refraction shadow, is a narrow band of decreased echoes that appears at the lateral edges of curved structures such as cysts, the gallbladder, the fetal skull, and large vessels. This artifact occurs because the ultrasound beam refracts, or bends, as it grazes the curved surface, diverting part of the beam away from its expected path and creating a shadow-like region. Edge shadows are important to recognize so that they are not mistaken for real pathology, such as a thickened wall or an adjacent lesion. Once understood, edge shadows can actually be helpful, as their presence at the edges of a round structure is one more confirming feature that the structure contains fluid.
Sonography Term