Visceral Vascular Tumors: Hemangioma and Hemangiosarcoma

What are visceral vascular tumors?

Visceral vascular tumors develop from blood vessels in the body’s internal organs, most commonly the heart, liver, and spleen, although they can also occur in other locations, such as the urinary bladder and intestines. Wherever there are blood vessels, vascular tumors may develop. The spleen, which filters blood, is the organ most commonly affected by these tumors.

There are two forms of visceral vascular tumors: 

• Hemangiomas are benign (non-cancerous) and can be thought of as large blood-filled growths, similar to blood blisters.
• Hemangiosarcomas are malignant (cancerous) and can spread to other parts of the body. 

What causes these tumors?

The reason why a particular pet may develop these, or any tumor, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.

While the cause of visceral vascular tumors in cats has not been determined, several genetic abnormalities have been identified in dogs. Certain large-breed dogs, such as German Shepherds, Labrador Retrievers, and Golden Retrievers, are particularly predisposed to developing hemangiosarcoma, although all sizes of dogs can develop this tumor. Hemangiosarcoma is a rare tumor in cats, accounting for less than 1.5% to 2% of non-blood cancers in this species.

What are the signs of these tumors?

The signs vary depending on the location of the tumor. Heart tumors may cause signs of heart failure, including:

• Lethargy
• Weakness
• Collapse
• Coughing
• Difficulty breathing
• Sudden death (if the tumor ruptures)

Tumors of the liver and spleen may rupture spontaneously, without any traumatic injury, and cause bleeding into the abdomen. Signs of internal bleeding include:

• Lethargy
• Weakness
• Collapse
• Decreased appetite
• Distended abdomen

If the bleeding is severe and untreated, it can be fatal. A ruptured tumor is a medical emergency and requires immediate veterinary attention.

How are these tumors diagnosed?

Veterinarians often diagnose visceral vascular tumors using ultrasound of the chest or abdomen, depending on the tumor's location. Based on the findings, your veterinarian may recommend surgery to remove the tumor or, in the case of a splenic tumor, remove the spleen. 

A veterinary pathologist examines the removed tissue under a microscope (histopathology) to determine the type of tumor. Up to 70% of dogs with splenic tumors have hemangiosarcoma. The remaining 30% may have a hemangioma or another type of tumor, such as lymphoma.

Your veterinarian should also perform staging (searching for spread to other locations in the body). This may include bloodwork, urinalysis, tests to evaluate blood clotting, X-rays, and abdominal ultrasound. If enlarged or abnormal lymph nodes are found during the physical examination or diagnostic testing, your veterinarian may collect samples to determine whether the cancer has spread.

How do these tumors typically progress?

Hemangiomas are the benign form of the disease and generally have a good prognosis. Although hemangiomas can rupture and cause internal bleeding, they are not known to spread to other parts of the body.

Hemangiosarcoma has a guarded (uncertain) to poor prognosis. In addition to the risk of sudden bleeding, hemangiosarcomas often spread (metastasize) to other parts of the body. These metastatic tumors can also rupture and bleed.

Hemangiosarcoma can spread to many organs, including the lungs, kidneys, muscles, spinal cord, and brain. The signs that develop depend on which organs are affected. For example, spread to the kidneys may cause increased drinking due to reduced kidney function.

How are these tumors treated?

Treatment depends on the type and location of the tumor. Surgery is the primary treatment, although chemotherapy may also be recommended for hemangiosarcoma.

Surgery

Surgery is the recommended treatment option for both hemangiomas and hemangiosarcomas. Surgery can prevent serious complications caused by tumor rupture and bleeding. However, surgical options may be limited with tumors of the heart. For tumors of the spleen, specifically hemangiosarcoma, a splenectomy (surgical removal of the spleen) is recommended. This procedure removes as much of the tumor as possible and helps prevent further bleeding. 

Chemotherapy

Because hemangiosarcoma has a high risk of spreading, chemotherapy is often recommended in addition to surgery. Chemotherapy may also be used as the primary treatment when surgery is not possible.

Is there anything else I should know?

If your pet has been diagnosed with a tumor of the spleen, the biggest risk is that the tumor could rupture and bleed, putting your pet at immediate risk. For that reason, it is very important to keep your pet quiet and monitor for any signs of bleeding listed above. In most cases, treatment should begin as soon as possible after diagnosis.

Anticoagulant medications or medications that may increase the risk of bleeding, such as nonsteroidal anti-inflammatory drugs (NSAIDs), should be avoided before surgery.