Large amount of fluid in the abdomen is always abnormal but has many causes. Often the fluid also extends into the pelvis. The medical term is ascites. The fluid can be simple fluid or complex and bloody. In practice, the most common causes for large amount of fluid are liver cirrhosis and cancer. Rarely I see a lot of fluid from bleeding. This happens because of trauma, surgery, or rupture of an aneurysm for example. Fluid can also be seen following surgery and inflammatory process like pancreatitis.
With liver failure and cirrhosis, there are varying amounts of fluid but can often be a large quantity. The fluid is often simple. The liver will look cirrhotic with nodular and bumpy contour. There will often be a history of cirrhosis, most commonly from alcohol abuse. The patient will often have multiple paracentesis where fluid will be withdrawn from the abdomen.
I see large amounts of fluid in patients with advanced cancer. Most commonly, I see this with ovarian cancer. Other cancers can also cause this when there is spread in the abdomen and pelvis, often to the lining or peritoneum. In many cases, other findings of cancer will be seen like nodules and masses representing spread of cancer. In ovarian cancer, there will usually be a mass in the pelvis representing the ovarian cancer.
Fluid from surgery is often in pockets. The major concern is abscess or walled off infection. This must be treated by draining it. Inflammatory process can cause large amounts of fluid. Most commonly this is from pancreatitis. There can be a large amount of fluid in the abdomen centered about the pancreas.
Large amount of bleeding is another concern when large amount of fluid is seen on CT. Usually the fluid will be denser then simple fluid. Often, there is concern from the clinical doctors about bleeding. The source of the bleeding is not always clear. In the setting of trauma, it is important to inspect the organs carefully for injury. A large aneurysm will be seen in the setting of ruptured aneurysm. Usually these ruptures are fatal. I’ve seen ovarian cyst ruptures cause large amount of fluid and bleeding.
While large amounts of fluid or ascites on CT are always abnormal, there are many causes. The clinical history and any associated findings on CT will be helpful to determine the cause. Liver cirrhosis and advanced cancer are probably the most common causes in my practice. Other causes include bleeding, post surgery and inflammation like pancreatitis.