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Hemangiopericytoma in Dogs

A hemangiopericytoma is metastatic vascular tumor arising from the pericyte cells, where hemangio refers to the blood vessels, and a pericyte is a type of connective tissue cell.

Hemangiopericytoma is malignant tumor that affects the cells surrounding the small blood vessels (capillaries) in subcutaneous tissue. A pericyte might best be described as a non-specialized cell. It is one of the original embryonic cells, but instead of taking on a specific function, it remains in its first stage, waiting until it is needed. The function of the pericyte is to differentiate into whatever type of cell the body requires to function, regenerating new tissue as needed. In this case, the pericyte is damaged by improper cell division, and instead of forming tissue that is useful to the body, it forms a tumor.

Although a hemangiopericytoma does not usually spread throughout the body, it does grow continuously at the the site of origin. Over the course of several months to possibly years, this deeply rooted tumor grows until it has taken up the space in which it resides, affected the nearby organs and eventually impairing their function. This can be especially fatal when it occurs in the chest, close to the heart and lungs. Fortunately, this tumor has a high rate of successful treatment, but it must be treated before it has grown to unmanageable proportions. Although relatively rare, metastasis is reported in about 20 percent of patients. In dogs this tumor is more common in large-breeds than in small-breeds.

Symptoms and Types

• Slow growing mass may be seen over weeks or months, usually on a limb
• Rapid growth in case of high grade variant tumor
• Soft, fluctuant or firm mass, usually on a limb, but in some cases on the trunk of the animal
• Small, but slowly growing bump or nodule on the body – may appear as an ulcer or sore, a bald spot, or as a differently pigmented (colored) area

Causes

The exact cause is still unknown.

Diagnosis

You will need to provide a thorough history of your dog's health leading up to the onset of symptoms. After the initial background information has been noted, your veterinarian will perform complete physical examination, which will include routine laboratory tests: a complete blood count, biochemistry profile, and urinalysis. The results of these tests are usually within normal ranges. A more definitive diagnosis will be based on the results of a biopsy analysis. Your veterinarian will take tissue a sample from the growing mass and examine it microscopically to confirm the diagnosis and determine the grade of the tumor. Your veterinarian may also take X-rays, computed tomography (CT) scans, or magnetic resonance imaging (MRI) scans to evaluate the extent of the local metastasis and how deeply rooted the tumor is. These studies will be key in planning the surgery and ongoing therapy for your dog.