Testing for Abdominal Enlargement in Dogs

What does abdominal enlargement mean?

Abdominal enlargement is a general term that means a dog’s belly is larger or fuller than usual and bulges beyond the normal outline of the body. Abdominal distension is another term that has a similar meaning but often refers to more severe cases of abdominal enlargement.

What are some causes of abdominal enlargement?

Abdominal enlargement may develop for many reasons depending on the age and gender of the dog. It can be a simple problem and even a normal condition in some pets. However, abdominal enlargement can also indicate serious underlying disease.

Simple causes of abdominal enlargement:

1. Intestinal parasites (worms). Large numbers of worms in the intestine can cause distension of the abdomen, giving a pet a pot-bellied appearance. This is typically seen in puppies, since they are more likely to have worms than older dogs. Simple treatment with de-worming medication usually cures the problem.
2. Obesity. Weight gain usually occurs when a dog eats too much or does not exercise enough, or both. Obesity leads to accumulation of fat in the abdomen and may result in abdominal enlargement. In dogs, obesity can also be a sign of hormonal imbalance.
3. Pregnancy. It is normal for pregnant female dogs to show abdominal enlargement by mid- to late pregnancy. Most dog owners know when their female dog has been bred and expect abdominal enlargement to develop. The easiest way to prevent pregnancy in non-breeding female pets is to spay them, preferably at a young age. If your dog is not spayed, be aware of when she is in heat (ready to mate) and you will be prepared for possible abdominal enlargement due to pregnancy.

Abdominal enlargement associated with illness:

1. Organ enlargement. An increase in size of one or more abdominal organs can cause the abdomen to appear distended. Organ enlargement is often a sign of underlying illness such as infectious disease, inflammation, tumors (cancerous or non-cancerous), and other conditions.
2. Free fluid in the abdomen. The accumulation of fluid in the abdomen is always a cause for concern. The free fluid can be urine or blood, or it can be an effusion(which is fluid that escapes from body tissues and collects in the abdomen). 
   • Free urine in the abdomen indicates the bladder, ureters, or urethra have been damaged and urine is leaking; this usually follows trauma such as being hit by a car. 
   • Free blood in the abdomen is associated with trauma, surgery, bleeding disorders, and some types of tumors. 
   • Effusions can develop for many different reasons such as liver disease, heart disease, abdominal tumors, and inflammation of the abdominal lining. Effusions should always be investigated to find the underlying cause.
3. Tumor/cancer. Tumors and cancers affecting abdominal organs often result in abdominal enlargement.
4. Heart disease. Heart failure can result in enlargement of the liver and cause free fluid to build up in the abdomen, resulting in abdominal enlargement.
5. Hypothyroidism. This disease develops when the thyroid gland fails to produce enough thyroid hormone. These dogs become sluggish and gain weight, even if they eat less and exercise. Fat builds up around the abdominal organs and over time leads to a bulging abdomen.
6. Cushing’s disease. This is a disorder of the adrenal glands, also known as hyperadrenocorticism. Affected dogs typically have abdominal enlargement due to enlargement of the liver, accumulation of fat in the abdomen, and a weakened body wall.
7. Gas buildup. In some dogs, especially large deep-chested breeds, including Great Danes, St. Bernards, and German Shepherds, large amounts of gas can get trapped in the stomach and intestines and cause serious abdominal distension. Sometimes the stomach and intestines become twisted, leading to a life-threatening condition that requires emergency surgery.

How do you determine the cause of abdominal enlargement in my dog?

The search for answers starts with a complete history and physical examination. Your dog’s history of illness refers to details about how long your dog has had abdominal enlargement, how quickly it appeared, and any event that might have occurred before you noticed the change.

"The search for answers starts with a complete history and physical examination."

For example, an overweight middle-aged dog with a history of slow gradual abdominal enlargement may have hypothyroidism (low thyroid hormone). In contrast, a young dog that has been hit by a car and has sudden abdominal distension is more likely to be bleeding into the abdomen. An accurate history gives your veterinarian important clues about the cause of the abdominal enlargement.

Physical examination involves thoroughly checking over the entire dog, listening to the heart and lungs with a stethoscope, and palpating the abdomen (gently squeezing or prodding the abdomen with the fingertips to identify abnormalities). A complete examination may detect heart disease, organ enlargement, an abdominal mass, the presence of free fluid or intestinal gas, and other abnormalities that could explain the abdominal enlargement.

History and physical exam are important, but further testing is usually required and your veterinarian may recommend doing screening tests. These are a series of simple tests that provide information about the overall health of the pet. The most common screening tests are complete blood count (CBC), serum biochemistry profile, and urinalysis.

What might these screening tests indicate?

A) Complete blood count. This is a simple blood test that provides information about the different cell types in blood. These include red blood cells, which carry oxygen to the tissues, white blood cells, which fight infection and respond to inflammation, and platelets, which help the blood to clot. The CBC provides details about the number, size, and shape of the various cell types, and identifies the presence of abnormal cells in circulation. See handout "Complete Blood Count" for further information.

The CBC might reveal a decrease in the number of red blood cells in the blood, a condition called anemia. In a dog with abdominal enlargement, mild anemia could be a sign of hypothyroidism or other chronic disease. More severe anemia could signal bleeding into the abdomen due to trauma or an abdominal tumor. An increase in the number of white blood cells could indicate infectious disease, inflammation associated with a tumor, or accumulation of fluid in the abdomen.

B) Serum biochemistry profile. This is the chemical analysis of serum, which is the pale yellow liquid part of blood that remains after the cells and clotting factors have been removed. There are many substances in serum, including proteins, enzymes, fats, sugars, hormones, electrolytes, etc. Measuring the levels of the various substances in the blood provides information about the health of the body’s organs and tissues such as the liver, kidney, and pancreas, and helps to detect diabetes. See handout "Serum Biochemistry" for further information.

In dogs with abdominal distension, abnormal biochemistry results may indicate which organ is affected and what the problem might be. Some examples are:

• Abnormally high levels of the liver-related enzymes alanine aminotransferase (ALT), alkaline phosphatase (ALP), and gamma glutamyltransferase (GGT) which could signal underlying liver disease or possibly Cushing's disease.
• Very low levels of albumin (a blood protein) can cause fluid to accumulate in the abdomen and could explain abdominal distension.
• High levels of serum globulin (proteins produced by the immune system) could signal underlying inflammation, infection, or cancer.
• A high level of cholesterol in a dog could be a clue for underlying hypothyroidism.
• Very low blood sugar levels could be a sign of insulinoma (a cancer of the pancreas).

C) Urinalysis is a simple test that analyzes the chemical and physical properties of urine. A urinalysis is important in any sick pet and is necessary for the proper interpretation of the serum biochemistry profile, especially in a pet that has kidney disease or diabetes. See handout "Urinalysis" for further information.

What other tests might be done to investigate abdominal enlargement?

Depending on the results of the history, physical examination, and screening tests, additional testing could include:

1. Specific blood tests. Specialized blood tests may be used if a particular disease or illness is suspected. There are many specialized tests including dexamethasone suppression and/or ACTH stimulation tests to confirm Cushing's disease; serum bile acid testing to detect liver disease; antibody tests for specific infectious diseases; thyroid hormone tests to diagnose hypothyroidism; and pregnancy tests in females that may have been bred.

2. Imaging studies. Radiographs (X-rays) and ultrasound are often recommended to assess internal organs and to look for possible abdominal masses. More sophisticated techniques such as magnetic resonance imaging (MRI) and computed tomography (CT scan) may also be recommended if they are available.

3. Testing for heart disease. This could involve radiographs, ultrasound, electrocardiogram, and blood tests such as ProBNP.

4. Biopsy. Biopsies may be taken if free fluid in the abdomen or a tumor is suspected. Free fluid in the abdomen is easily collected by fine needle aspiration, which involves passing a sterile needle through the body wall into the abdomen. A sterile syringe is attached and gentle suction is used to remove a small amount of fluid. The collected fluid is sent to the laboratory to be analyzed by a veterinary pathologist. Masses or enlarged organs may be sampled by fine needle aspiration or tissue biopsy.

Both types of samples can be collected through the skin with the help of ultrasound, or collected directly during surgical exploration of the abdomen. Collected tissue samples are sent to the laboratory for analysis by a veterinary pathologist.