A common term used by radiologists across all different types of tests is a filling defect. This means that there is something inside a lumen that prevents normal filling. A spot that looks different from everything else inside a lumen. This term does not necessarily mean that the structure is abnormal.
A filling defect is commonly used when contrast or dye is given. One example would be when barium contrast is given by mouth for an upper gastrointestinal study. The barium normal fills the tube like esophagus throughout. It normally looks white throughout on X-ray because of the barium. A filling defect would be a dark spot somewhere in the esophagus amongst the white of the swallowed barium. The filling defect just means that something is preventing the white barium from covering that area. Usually something that occupies space.
Another example would be a CT done to look at the bladder. In this case, contrast is given through a vein. When contrast reaches the bladder after a delay, it usually outlines the bladder which looks white on the CT. A dark spot surrounded by contrast would be called a filling defect. The dark spot takes up space and prevents the contrast from covering that area. The filling defect can be many things such as a tumor, stone, herniation in addition to other things.
A CT done to look for clots to the lungs or pulmonary arteries is done after giving contrast or dye through a vein. The pulmonary arteries look white throughout. A clot to one of the pulmonary arteries would look like a filling defect. A dark area amongst the white of the pulmonary arteries. This can be in one artery or many.
An example where no contrast is given would be a study to look for stones in the common bile duct called an MRCP. The bile duct connects the liver to the intestine. This is where bile flows to help with food digestion. A stone, tumor or other abnormality on this study will look like a filling defect. The bile is normally white on this study. A stone will look black and would be a filling defect amongst the white of the bile.
There are many other examples of filling defects. Radiologists may use this phrase anytime there is something in a lumen. This does not necessarily mean that there is an abnormality. Sometimes this can be caused by normal structures or even artifacts which aren’t real. Filling defects may need additional testing to determine the cause. This can be another imaging test or a more invasive procedure. The term is helpful in that it alerts the referring doctor that something is present which may be abnormal.