Small amount of free fluid in the pelvis is a common finding on pelvic CT. This is often a normal finding in women related to ovulation. In men, it is a bit more concerning but a small amount can still be within normal limits. The clinical setting of the free fluid is also important to consider.
A small amount of free fluid in reproductive age women is normal. This is particularly true if there are no associated abnormal findings like prior trauma, cancer or inflammatory process like appendicitis. In men, the first thing that comes to mind is an inflammatory process like appendicitis or inflammatory bowel disease.
Small amount of free fluid in the pelvis with a history of trauma becomes more significant. I usually measure the density of the fluid to determine if it represents blood. In women, a small amount of blood related to ovulation can be normal. But if I see it in the setting of trauma, I look carefully for any injuries to the organs and bowel. In men, this would be more concerning. Even if no injuries are found on CT, an injury could still be present.
Small amount of free fluid can also be related to an inflammatory process like appendicitis or diverticulitis. In this case, the CT will show the abnormal inflammatory process and some associated fluid in the pelvis. The free fluid in the pelvis is most commonly a secondary finding.
A small amount of free fluid can also be seen in the setting of cancer. In these cases, cancer findings will be seen and often spread to the lining of the abdomen and pelvis called the peritoneum will be seen. Usually, the fluid is a secondary finding. In many cases, the cancer will be known.
Therefore, a small amount of free fluid in the pelvis is most commonly normal. However, depending on whether it’s a man or women, and the clinical setting, other concerns are raised. In many cases, the fluid is an associated finding and the primary abnormality, whether it be inflammatory, related to liver cirrhosis, traumatic or cancer will be seen.