Fluid Collection in the Abdomen on CT

Fluid collection in the abdomen has many different causes.  This means the collection is organized and not free flowing.  Fluid collections can be of various consistencies, from simple fluid to pus.  These collections are frequently imaged on CT.  The origin of the collection can sometimes be identified from the CT which would help with treatment.

Ascites is the most common collection I see although this is usually not organized.  It is free flowing but can be loculated at times.  The most common cause is either cirrhosis or advanced cancer.  There can be small amounts or tense large ascites filling the entire abdomen and pelvis.  The cause of the ascites can sometimes be identified by findings of cancer or liver disease.

Seromas or post operative collections of fluid are common.  For example, there is often fluid in the gallbladder surgical bed after cholecystectomy.   These resolve over time on their own.  It is not possible to tell if these collections are infected on imaging in many cases.

Urinomas are collections of urine which has leaked from an injury to the kidney or ureter.  I see these sometimes when the kidney becomes obstructed from a passing kidney stone or after kidney surgery or procedures.   These collections are usually in close proximity to the kidneys and ureters.  These may need to be drained when they are large.

Bilomas are collections of bile that have leaked.  Bile is made by the liver, stored in the gallbladder and is delivered to the intestine to help with digestion through the bile ducts.  Injury to the ducts which delivers bile to the intestines can result in a biloma.  A biloma looks like a fluid collection near the bile ducts.  Treatment can be with drainage.  The diagnosis can be confirmed with additional testing like a nuclear medicine HIDA scan.

Hematomas or collections of blood and can be from multiple causes.  Sometime this is related to trauma.  In these cases, organ injury may be seen on the CT.  Hematomas can also be seen after surgery as a complication.  Hematomas in the abdomen can form when an organ is bleeding or when a mass within an organ like the kidneys is bleeding.  They can form when an aneurysm ruptures.

An abscess can form in the abdomen from many causes and in many locations.  An abscess is an infected collection of pus.   Abscesses are usually thick walled collections with bubbles of gas inside.  Abscesses can form from an inflammatory process like diverticulitis or appendicitis to name a few.  They can occur after surgery or procedures.  Abscesses are often promptly treated with antibiotics and drainage.

A fluid collection in the abdomen on CT has many causes.  The patient’s history, appearance and location on CT gives clues to the diagnosis.  In some cases, sampling will be needed when infection is suspected.   Some collections can be left alone while others like bleeding and abscess require prompt treatment.    CT plays a key role in both diagnosis and treatment.