Fat stranding means that the normally dark fat is replaced by a brighter fuzzy appearance. This can be a small area or involving most of the pelvis. Fat stranding is an important finding that identifies an abnormality on CT. Fat stranding can be from many causes but most commonly inflammation. It can also be seen after trauma, surgery, cancer, scarring, in addition to others.
Fat stranding in the pelvis can be found anywhere. It can be around the ovaries, the bowel, the blood vessels, along the skin and the appendix which sometimes go down to the pelvis. One of the more common causes is when you get diverticulitis of the colon. The sigmoid colon is located in the pelvis and an inflamed diverticulum or out pouching of the wall will give rise to fat stranding.
Appendicitis is another common cause of fat stranding in the pelvis. Sometimes the appendix extends into the pelvis. When it becomes inflamed, there will be fat stranding around it. Stranding around an ovary can occur when it is inflamed or twisted. Inflamed ovaries can be seen with pelvic inflammatory disease. A twisted or torsed ovary will be large and swollen with surrounding standing. Sometimes when a cyst ruptures, you will get stranding around it as well as fluid.
Stranding can also happen after trauma. Like when there is bruising to the skin or abdominal wall. Stranding is also seen throughout the pelvis if you image a patient after surgery like hysterectomy. Stranding can also be seen after a Caesarian section around the uterus and skin where the incision is made.
Stranding in the pelvis on CT can also be seen with cancer. Most commonly I see stranding when a patient has ovarian cancer and there is spread to the omentum which is just deep to the abdominal wall. Spread of cancer from a mass can also look like stranding in the adjacent fat. A clotted vein in the pelvis can sometimes have stranding around it.
While stranding can be seen with many conditions, often there are other findings that help with the diagnosis. The radiologist in many cases will be able to provide a precise diagnosis based on the history, prior scans, and any other imaging findings. The location and extent of fat stranding in the pelvis will also help with the diagnosis.