MRI is frequently done to image the pelvis for a variety of reasons. Pelvic MRI in women is commonly done to image the uterus and ovaries. In men, imaging is commonly done to look at the prostate. Other reasons include cancer staging, bowel imaging and after surgery amongst many other causes.
A small amount of fluid in the pelvis is a common finding seen on many exams. It is most common to see this as an incidental finding. This means that it is not the reason for symptoms and may not have any clinical significance. Usually the fluid is best seen along the dependent pelvis.
A small amount of fluid in the pelvis on MRI in women is a normal finding that is related to ovulation. This often layers in the dependent pelvis and has a simple or hemorrhagic appearance. Assuming no other concerning findings or clinical history, this can be assumed to be a normal expected finding. A small amount of free fluid in the pelvis in men and women who are post menopausal is more concerning for abnormality but can still be normal.
A small amount of free fluid in the pelvis on MRI can be seen with inflammatory conditions of the pelvis. Examples would include diverticulitis of the colon or pelvic inflammatory disease. An appendix that is inflamed in the pelvis can cause free fluid. Free fluid in the pelvis can be seen with liver disease and cirrhosis.
A common cause of free fluid in the pelvis on MRI is a ruptured cyst. This can results in small to large quantities of fluid. The fluid may be bloody if a hemorrhagic cyst ruptures. Some women may need surgery if the bleeding results in drop in blood pressure and shock.
Trauma is another cause of free fluid in the pelvis on MRI. Trauma is much more commonly imaged with CT however. The free fluid in the pelvis is more suspicious if it is bloody and larger in quantity. Injury may be to the organs, bowel and supporting structures. Imaging of the abdomen may be needed to define the injuries.
Cancer can result in free fluid in the pelvis. This is often in advanced cancer that has spread to the abdominal lining. Often there will be a known history of cancer. There will be other findings that indicate cancer. This is commonly seen with ovarian and gastrointestinal cancers.
A small amount of free fluid in the pelvis on MRI has many causes. It is often a normal finding. This is particularly true if there is no concerning history or other abnormal findings. In cases where it is abnormal, the underlying condition needs to be diagnosed. This can sometimes be seen on the imaging or obtained from the history.