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 will vary in each individual case. For example, a cat with ascites and a history of trauma (falling from a height, or being hit by a car) could have internal bleeding or a ruptured bladder, with the fluid in the abdomen being blood or 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.
Causes of Enlarged Abdomens in Cats
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. In kittens, intestinal parasitism may cause an enlarged appearance to the abdomen.
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 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.
Your Cat Needs an Ultrasound for Ascite Diagnosis
Determining the cause of the ascites will require 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, does allow for confirmation of the presence of fluid, and also enables the veterinarian to evaluate the other abdominal organs, e.g. the liver, spleen and pancreas for potential causes of ascites. In fact, abdominal fluid enhances the images seen on ultrasound, allowing for better detail.
Analysis of the abdominal fluid can be very helpful in determining a cause for the ascites. A sample can be obtained by inserting a small needle into the abdomen, and withdrawing some fluid with a syringe. This technique — called abdominocentesis — 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 abdominal fluid may be partially reabsorbed back into the bloodstream. In cases of hemorrhage, as many as 50 percent of the red blood cells can go back into the circulation.
Feline Abdominal Fluid Classifications
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, but because there is a lot of overlap between categories, most practitioners don’t find this classification very useful.
A more practical classification attributes the ascites to one of seven disease categories: cardiac, cancer, liver, feline infectious peritonitis (FIP), kidney, urinary tract trauma and peritonitis (inflammation of the lining of the abdomen).As compared to dogs, heart disease isn’t a major cause of ascites in cats. 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.
Ascites Are Often A Sign of Disease
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. If the tumor metastasizes throughout the entire abdomen — a condition called carcinomatosis — it often leads to ascites.
Feline infectious peritonitis (FIP) is a terrible viral disease that commonly causes abdominal fluid accumulation. Cats of any age are susceptible, although young cats are more commonly affected. Although extensive research into therapy for FIP is currently underway, FIP is still not treatable and cats invariably succumb to the disorder.
Severe liver disease can also 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. Unfortunately, this can lead to ascites.
Additionally, 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, but improved ultrasound equipment and the development of a blood test called the fPLI test has made diagnosis easier.
Managing Your Cat’s Ascites
Unfortunately, ascites often occurs at the end stages of disorders that cannot be cured. At that point, the focus of treatment involves trying to manage the ascites rather than resolve it. Medical management of the underlying condition — such as heart or liver failure — may decrease the amount of ascites present and reduce the formation of additional fluid. In most instances, however, medication stabilizes the underlying disease, but will have minimal effect on the abdominal effusion. In these cases, fluid can be removed from the abdomen periodically, relieving the discomfort of a distended abdomen.
Sadly, the disorders that cause ascites in cats tend to be ominous, and the prognosis is usually guarded or poor. 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.