Fat stranding on CT describes the fat next to a structure looking lighter and dirtier than the usual homogeneous dark gray found throughout the body. Often fat stranding on CT is seen around an inflamed structure but can also be seen with infection, trauma, cancer and following surgery. Fat stranding is an important finding that alerts the radiologist to an abnormality. Fat stranding can be seen throughout the body.
Fat stranding on CT often indicates an inflammatory process. One of the more common examples being acute appendicitis. When the appendix becomes inflamed, the surrounding fat becomes brighter and dirtier looking. This is one of the best signs for appendicitis. Many other inflammatory conditions also lead to the same finding to include inflamed gallbladder, pancreas, colon, and kidney. Fat stranding can also be seen when you have infection of the skin or adjacent tissues (cellulitis). Often fat stranding is not the only finding to indicate an abnormality of these organs, but one of the most important.
Fat stranding is also seen after trauma. Bruising often looks like stranding under the skin. Injury to an organ can also look like stranding. Often there is fluid or blood surrounding the organ and possible internal injury as well. There is often stranding around a bone when it breaks. There is stranding around a site that is bleeding from trauma.
Fat stranding on CT can also be seen with cancer. Sometimes when a cancer spreads to adjacent parts of the body, you will see stranding. A pancreatic tumor which is spreading to nearby parts can have stranding in the tissues, in addition to other findings. When tumor spreads to the lining of the belly (peritoneum), there can be stranding next to the lining or peritoneum. Stranding can also be seen next to a tumor after treatment.
Fat stranding on CT can also be seen after surgery or procedures. Often there will be stranding around the site of surgery and under the skin where the incision was made. Fat stranding can often persist for some time after the surgery. Post operative infection can also look like fat stranding so the distinction on imaging may not be possible. Scarring after surgery can also look like fat stranding either around the surgical site or at the skin. There is often stranding at the skin puncture site after invasive procedures like a heart angiogram or biopsy.
Fat stranding can also be seen when there is edema or fluid accumulation. This is often seen around the kidneys and in the back part of the abdomen and pelvis called the retroperitoneum. Edema or fluid can also accumulate under the skin throughout the body called anasarca. This can be seen when there is poor function of organs such as kidneys or heart.
Fat stranding on CT is therefore a common finding but one which is sometimes not specific for a particular diagnosis. The radiologist who interprets the scan will use any other findings including your personal history to make a diagnosis. Sometimes fat stranding is an indicator of a precise diagnosis such as appendicitis while other times, it can mean a range of possibilities.