Ascites (abdominal effusion) in Cats


Accumulation of fluid in the abdomen is an important sign of illness in cats

            Ascites (pronounced “a-site-eez”) is the accumulation of fluid in the abdominal cavity.  It is a sign of disease, rather than a diagnosis.  Unfortunately, there are very few benign causes of ascites. 

            Because there are so many possible causes of ascites, the historical findings vary in each individual case.  For example, a cat with ascites and a history of trauma (falling from a height, or hit by a car) could have internal bleeding, the fluid in the abdomen being blood, or a ruptured bladder, the fluid being urine.  Cats with labored breathing and exercise intolerance could be suffering from heart disease, another potential cause of abdominal fluid accumulation.  It is therefore important to get an accurate history from the cat owner as to the cat’s appetite, behavior, travel history, potential for trauma, etc.

            Cats with ascites are usually presented to the veterinarian with a complaint of abdominal distention.  However, there are other causes for a big belly in cats besides fluid accumulation, for example, abdominal tumors, enlarged organs such as a big liver or a big spleen, or an enlarged bladder due to a urinary obstruction.  The physical examination may yield other clues as to the cause of the ascites.  Cats with a heart murmur and weak pulses may have heart failure as the cause of their ascites.  Cats with peripheral edema (swelling of the limbs) may indicate that a low protein level in the bloodstream, another cause of fluid accumulation.   Some cats don’t seem to be bothered by ascites, while others are clearly uncomfortable.  Much depends on the volume of fluid that has accumulated.  Large amounts of fluid can put pressure on the diaphragm, limiting the expansion of the lungs and making it difficult to breathe.

            Determining the cause of the ascites requires various diagnostic tests.  X-rays of the abdomen are not very useful because the presence of fluid obscures the details of the other abdominal organs.  Abdominal ultrasound, however, allows for confirmation of the presence of fluid, and allows the veterinarian to evaluate the other abdominal organs, e.g. the liver, spleen and pancreas for potential causes of ascites.

            Analysis of the abdominal fluid can be very helpful in determining a cause for the ascites.  A fluid sample can be obtained by inserting a 20 or 22-gauge needle into the abdomen and withdrawing a sample with a syringe.  This technique is more successful when there’s a large volume of fluid present.  If there’s only a small volume of fluid present, ultrasound may help localize the fluid, allowing for successful sampling.  Most cats with ascites do not require complete removal of all fluid.  In some patients, the increase in pressure inside the abdomen from the fluid build-up actually prevents further accumulation, and if a lot of fluid is removed, it may re-form rapidly.  This can lead to a rapid decrease in the blood volume, leading to cardiovascular collapse and shock.  If the amount of fluid present is causing respiratory difficulty, enough fluid should be removed so that breathing is no longer compromised.  Fluid samples should be sent to a clinical pathologist for evaluation.

            If the underlying cause of the fluid can be identified and corrected, the fluid may be partially reabsorbed back into the bloodstream.  In cases of hemorrhage, as many as 50% the red blood cells can go back into the circulation. 

            Clinical pathologists often classify the fluid into one of three major categories: exudate, transudate, or modified transudate, based on the amount of protein and cells in the fluid.  Most samples end up being modified transudates, however, there is a lot of overlap between categories, and most practitioners don’t fine this classification very useful.  A more practical classification attributes the ascites to one of 7 disease categories:  cardiac, cancer, liver, kidney, urinary tract trauma, feline infectious peritonitis (FIP), and peritonitis (inflammation of the lining of the abdomen).

            Heart disease isn’t a major cause of ascites in cats, compared to dogs.  Prior to 1987, heart disease was a significant cause of ascites in cats, mainly due to the disease dilated cardiomyopathy (DCM), which was fairly prevalent.  Once it was discovered that a deficiency in the amino acid taurine was the primary cause of feline DCM, pet food manufacturers corrected the deficiency in the food and the incidence of DCM dropped dramatically. 

            Sadly, cancer is a common cause of abdominal effusion in cats, and is more common as cats get older.  In most cases, the initial tumor is a carcinoma, typically involving the gastrointestinal tract or pancreas.  The tumor metastasizes throughout the entire abdomen, a condition called carcinomatosis, and this often leads to ascites. 

            Feline infectious peritonitis (FIP) is a terrible viral disease that commonly causes abdominal fluid accumulation.  Any age cat is susceptible, although young cats are more commonly affected.  Unfortunately, FIP is not treatable and cats invariably succumb to the disorder. 

            Severe liver disease may cause ascites in cats.  The liver produces albumin, a protein that is important in helping maintain fluid within the circulation.  If the liver is very diseased, it may produce inadequate amounts of albumin, resulting in hypoproteinemia, a reduced level of protein in the blood.  This can lead to ascites.

            Pancreatitis is a common cause of ascites in cats.  In acute, severe cases of pancreatitis, fluid leaks through the vessels within the inflamed pancreas, into the abdominal cavity.  Pancreatitis used to be difficult to diagnose in cats, however, better ultrasound equipment and the development of a blood test called the fPLI test has made pancreatitis less difficult to diagnose. 

            Unfortunately, the disorders that cause ascites in cats tend to be bad, and the prognosis is usually guarded or poor.  Cat owners who think their cat might have a distended or enlarging abdomen should seek veterinary advice immediately, as early detection and prompt diagnosis may lead to a better outcome. 

Possible causes for ascites

Trauma and internal bleeding
Blood clotting disorder
Bleeding tumor
Urinary tract rupture
Feline infectious peritonitis
Heart disease
Liver failure

Hypoproteinemia (low serum blood protein)