Enlarged Spleen in Dogs: 7 Causes

An enlarged spleen in dogs can happen for a variety of reasons—and there aren’t always a lot of warning signs. To help you better understand your dog’s condition, integrative veterinarian Dr. Julie Buzby discusses the top seven causes of an enlarged spleen in dogs and explains what the diagnostic and treatment process involves.

Whenever I tell a client that their dog has an enlarged spleen, the next questions tend to be, “What caused this?” and “What does this mean for my dog?”

These are good questions, and ones I strive to answer to the best of my abilities. Usually, I start out by briefly discussing the causes of an enlarged spleen. Then we can talk about the next steps for their dog.

As I tell my clients, in order to understand why the spleen may become enlarged, it helps to first understand what the spleen does.

What is the spleen?

The spleen is a long, slender, reddish organ that normally lies on the left side of your dog’s abdomen near the liver and stomach. One end is attached to the stomach by a mesh of blood vessels and connective tissue, and the other end can move freely. Three main components—blood vessels, red blood cells, and white blood cells—make up the bulk of the spleen and help it perform its important jobs.

Store blood components

I like to compare the spleen to a sponge because it stores 10 – 20% of a dog’s blood volume at any given time. If the body suddenly needs more blood, for example after a traumatic injury, the spleen can contract and squeeze out blood components.

Make red and white blood cells and platelets

In addition to storing blood, the spleen is also capable of producing red blood cells, white blood cells, and platelets. Normally the bone marrow, not the spleen, is responsible for making the majority of the new blood cells. But having the spleen as an additional “cell factory” is useful, particularly when there is a high demand for new cells.

Filter the blood

Finally, the spleen also filters all the blood in a dog or cat’s body. This means it can perform “quality control” by removing any old or damaged red blood cells. Plus, it will pull out disease-causing agents or infected cells and then work with the rest of the immune system to mount a response to that invader.

What causes an enlarged spleen in dogs?

Based on this description of the spleen’s duties, you can probably make some guesses as to what sorts of things make the spleen get bigger. They include:

• More cells (i.e. discrete masses or other cells invading the spleen)
• An increased workload in response to infection or cell destruction
• Trapped blood in the blood vessels (i.e. blood gets in but can’t get out)
• Bleeding into the tissue of the spleen

Some of these processes will make the spleen, as a whole, get bigger. This is called “diffuse enlargement.” Others will cause a distinct nodule or mass in one or more locations (i.e. focal or multifocal enlargement).

To help make this information more concrete, let’s take a closer look at the specifics of seven of the most common conditions that would lead to splenomegaly in dogs (i.e. an enlarged spleen in dogs).

#1: Splenic masses

By far, the most common reason for an enlarged spleen in dogs is a splenic tumor. I wrote an entire article about splenic masses in dogs, so I’ll just hit the high points for you here.

Splenic masses can either be benign or malignant, but both types have the potential to rupture and bleed profusely into the abdomen. This can be life-threatening and means you may need to make some hard decisions in a short amount of time.

If your vet suspects your dog has a splenic mass, he or she can give you specifics about your dog’s case. Additionally, you may find these statistics helpful:

1. As a general rule, if the mass is bleeding, it will be malignant in two-thirds of dogs. And of those dogs, another two-thirds will have a specific aggressive blood vessel cancer called hemangiosarcoma in dogs. Unfortunately, the prognosis for dogs with splenic hemangiosarcoma is poor. This means that often sooner, rather than later, dog parents need to wrestle with the question of when to euthanize a dog with hemangiosarcoma.
2. On the other hand, around 70% of splenic masses that are not ruptured (i.e. not bleeding) are benign. So if your vet happens to find a mass on your dog’s spleen during a routine exam or diagnostics for another condition, there is a 70% chance that it isn’t cancer. The most common masses that would fall in the benign category are hematomas (i.e. blood clots) and hemangiomas (i.e. benign blood vessel masses).

#2: Cancer

While, as we just discussed, some dogs have a distinct cancerous mass on their spleen, other dogs with cancer have a more uniformly enlarged spleen. This occurs because cancer cells are infiltrating the whole spleen rather than grouping together to form a mass. Cancers that can cause diffuse splenic enlargement includes:

• Lymphoma in dogs
• Multiple myeloma
• Mast cell tumors in dogs
• Leukemia

#3: Inflammation of the spleen

Sometimes an immune response to severe viral or bacterial infections or parasite infestations can lead to splenic enlargement. After cancer, this is the next most common cause of splenomegaly.

As you know, the spleen plays an important role in the immune system by filtering pathogens out of the blood. Plus, it helps mount an immune response to these “foreign invaders.” Therefore, when the spleen is working hard to fight an infection, it can swell up due to the extra immune system cells.

An enlarged spleen may occur in infectious conditions such as:

• Hepatitis (i.e. inflammation of the liver due to infection, which can cause an enlarged liver and spleen in dogs)
• Pyometra in dogs
• Sepsis

#4: Autoimmune conditions

Splenomegaly also occurs in dogs with immune-mediated hemolytic anemia (IMHA in dogs) and immune-mediated thrombocytopenia (ITP in dogs). In these conditions, the body marks its red blood cells (IMHA) or platelets (ITP) as being “foreign.”

As we discussed, the spleen is one of the organs responsible for pulling “abnormal” cells out of circulation. This means it has to work overtime in IMHA or ITP. Plus, the spleen has to ramp up the production of new blood cells to replace the ones it is destroying. The combination of these two processes leads to the enlargement of the spleen.

#5: Congestion

Another common cause of splenomegaly is congestion. As the name implies, congestion occurs when some of the many blood vessels associated with the spleen become “backed up.” Blood still may be entering the spleen but it can’t get out. Thus, it starts to build up, just like traffic does when a few lanes of the highway are closed. This disturbance in blood flow can cause damage to the spleen and possibly other organs.

Common reasons for splenic congestion include:

• Liver disease in dogs
• Right-side heart failure from heartworm disease in dogs or other causes of heart disease in dogs
• Certain anesthetic or sedative medications (this congestion is just temporary)
• Splenic torsion (which we will talk about next)

#6: Splenic torsion

Remember how I told you that the spleen is attached to the stomach at one end? Well, sometimes when the stomach rotates into an abnormal position, as is the case with GDV (gastric dilation volvulus) or bloat in dogs, the spleen can become twisted too.

Additionally, dogs, especially those with deep chests like German Shepherds, may have a primary splenic torsion (i.e. one that happens spontaneously). This may be either acute, with sudden onset of severe symptoms, or more chronic, with a slower onset of non-specific symptoms.

In either situation, the twisting of the spleen can cause the spleen to swell. Plus, it can compress blood vessels and prevent blood flow. This can lead to the splenic tissue becoming congested and damaged or potentially even death.

#7: Trauma to the spleen

The spleen is a “sensitive” organ and can be easily injured. In cases of trauma, like when a dog is hit by a car, it is possible for the spleen to be damaged or even rupture. Sometimes in less forceful trauma, the spleen can also form a hematoma. This is essentially a “bruise” or blood blister in the splenic tissue.

What are the symptoms of an enlarged spleen in dogs?

As you can see, there are a variety of different causes of an enlarged spleen. Some, like trauma or a GDV, usually have pretty abrupt and obvious signs. However, a splenic tumor can and often does, hide until it ruptures. Therefore, there isn’t really one set of symptoms that can indicate a dog has an enlarged spleen.

Instead, there are some non-specific signs that could go along with splenomegaly (and a variety of other conditions too). They include:

• Painful abdomen (which can also occur in conditions like pancreatitis in dogs)
• Vomiting
• Diarrhea
• Decreased appetite
• Being a lethargic dog/decreased energy
• Weakness
• Weight loss
• Dog has a pot-bellied appearance

If you see any of these signs or have other concerns, please make an appointment with your veterinarian.

Keep in mind, too, that some dogs with an enlarged spleen have no clinical signs. The vet may end up discovering your dog’s spleen is bigger than normal while palpating the abdomen. Or the splenomegaly may show up on an X-ray or other imaging the vet performed for a different reason.

Signs of a spleen emergency

Alternatively, with a ruptured splenic mass, splenic torsion, or other serious conditions, the signs may be sudden and severe. Symptoms that point toward a life-threatening problem include:

• Pale or white gums due to shock or anemia in dogs
• Weak pulses
• Labored breathing
• Collapse or being unresponsive

If you see any of those signs, immediately make an emergency vet visit. Left untreated, these conditions can rapidly become fatal.

How does the vet diagnose an enlarged spleen?

During the visit, the vet will start with a physical examination. This allows him or her to:

• Look at your dog’s gum color
• Assess your dog’s vital signs
• Palpate your dog’s abdomen
• Evaluate the rest of your dog’s body for bruises, lumps, signs of trauma, or other clues

Based on the findings (and how stable your dog is) the vet may recommend various diagnostics.

Bloodwork

The vet may use bloodwork to get a better idea of what is going on with your dog. The complete blood count (CBC) can allow the vet to look for signs of infection, low platelets from ITP, low red blood cells from IMHA, or internal bleeding. And the chemistry panel can help rule in or rule out other conditions with similar nonspecific signs like kidney failure in dogs or liver disease.

Urinalysis and fecal examination

A urinalysis is a good way to look for infections like UTIs in dogs or pyelonephritis in dogs. Plus, a fecal test for dogs can help rule out parasites.

Abdominal X-rays

An X-ray (i.e. abdominal radiograph) can help your vet to evaluate the size, shape, and position of the spleen. Plus, it allows him or her to see the other abdominal organs and look for a gas-dilated and twisted stomach that would indicate a GDV.

Abdominal ultrasound

An even better way to take a look at a potentially enlarged spleen is an abdominal ultrasound. It allows the vet to get a detailed view of the architecture of the spleen and surrounding organs. The ultrasound may reveal:

• Splenic masses
• Splenic torsion
• Congestion
• Infiltration by other cells (e.g. lymphoma)
• Free blood in the abdomen from a ruptured splenic mass or trauma

Fine-needle aspiration

While performing the ultrasound, your veterinarian may want to do a fine needle aspirate (FNA) of the spleen. He or she will start by using the ultrasound to visualize the area of interest in the spleen. Then the vet will insert a needle under ultrasound guidance to collect a sample of cells from the spleen.

Examining these cells under the microscope can sometimes help the vet reach a diagnosis. Other times, it may be inconclusive.

Biopsy

Either way, if the vet needs to remove the spleen, he or she will probably also recommend a biopsy. This lets the veterinary pathologist look at slices of tissue, not just cells (like in an FNA). For this reason, a biopsy is a more definitive way of figuring out what was going on with the spleen. It can also indicate if a mass was benign or malignant.

What is the treatment for an enlarged spleen?

Once the veterinarian determines why your dog has an enlarged spleen, he or she will talk with you about the various treatment options. They are going to differ depending on your dog’s condition, but some possible treatments may include:

Splenectomy

This surgery involves removing the spleen and tends to be a common treatment for splenic masses. If the mass has ruptured, a dog may require an emergency splenectomy to control the bleeding. However, if the splenic mass was an incidental finding, the dog can have a scheduled (non-emergency) splenectomy.

Splenectomy is also the treatment of choice when there is a diagnosis of splenic torsion and in some cases splenic trauma. (For a feel-good story about a police dog with a splenic torsion, check out this news release from the University of Illinois College of Veterinary Medicine.)

There are some risks associated with the surgery itself such as bleeding and abnormal heart rhythms. However, the good news is that a dog can live without a spleen.

What that life looks like depends on why they needed the splenectomy in the first place. If the mass was benign or the dog had a splenic torsion, the prognosis is going to be significantly better than if the dog had a malignant mass.

Medications

If the dog has an immune-mediated disease like ITP or IMHA, he or she may need to be on prednisone for dogs or other immunosuppressants. Some dogs are able to get off these medications eventually, while others require lifelong treatment.

Alternatively, if an infection is a culprit, the dog may need antibiotics. Or the dog may benefit from heart medications if right heart failure is causing blood to back up into the spleen.

Chemotherapy (or other cancer treatments)

Sometimes the parents of dogs with hemangiosarcoma, lymphoma, or other types of cancer may decide to pursue chemotherapy. This may buy a few more weeks or months together (or occasionally longer). A board-certified veterinary oncologist can advise you about the pros and cons of chemotherapy or other treatments for your dog’s particular cancer.

Supportive care

Additionally, dogs may benefit from various additional therapies. This might mean IV fluids and a blood transfusion to stabilize a dog with a bleeding splenic mass. Or it could be Cerenia for dogs or appetite stimulants for dogs if your dog is nauseous or not eating well.

What is the life expectancy of a dog with an enlarged spleen?

As you have probably figured out from our discussion in the treatment section, the outlook for dogs with an enlarged spleen varies. Sometimes a family must prepare for their dog’s euthanasia within minutes, hours, days, or weeks of the diagnosis. Other times, the dog may have a splenectomy or take medication for a period of time and then never look back.

Therefore, your veterinarian is the best person to give you an idea of what to expect in terms of prognosis and life expectancy. He or she is familiar with your dog’s situation and would be happy to walk alongside you during this difficult time.

Stay strong in the face of an enlarged spleen in dogs diagnosis

I know it can be scary when your dog is diagnosed with splenomegaly. It’s easy for your mind to go right to the worst-case scenario or to feel hopeless.

However, I urge you to keep pushing forward and advocating for your dog. Work closely with your vet and follow his or her recommendations so you can get to the bottom of why your dog has an enlarged spleen. Then continue to lean on your vet’s expertise as you face whatever the future may hold for you and your dog.

What was the cause of your dog’s enlarged spleen?

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