Why is a lateral decubitus image of the abdomen ordered?

A lateral decubitus image of the abdomen is ordered primarily to visualize air-fluid levels. This positioning allows for differentiation between air and fluid present in the abdominal cavity. When a patient is in the lateral decubitus position, any free air will rise to the highest point, which is typically identified along the liver margins on the right side in a standard lateral view. This image is especially useful in detecting conditions like ascites (fluid accumulation) or free air due to perforation of a hollow organ.

While other considerations such as measuring organ size, checking for stones, or studying the vascular system are important in abdominal imaging, they are typically addressed through different imaging modalities or positions better suited to those objectives. For instance, kidney stones are usually evaluated through a CT scan or an upright abdominal X-ray, and vascular studies often require specialized imaging techniques. Thus, the ability of the lateral decubitus position to clearly show air-fluid levels is the distinguishing reason for utilizing this specific view in abdominal imaging.