Cancer of the Blood Vessel Cells in Dogs

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.

Treatment

Early and aggressive surgical excision of the affected tissue, along with some of the surrounding normal tissue remains the treatment of choice. A skilled veterinary surgeon will be called on to excise the affected area in order to enhance the chances of a complete removal of tumor. The removed tissue will be submitted to a veterinary pathologist for evaluation. Radiation therapy is generally highly successful with this type of tumor. You and your veterinarian will work together to decide if surgery along with radiation therapy is the best course of treatment for your dog.

In many cases, recurrence is expected, as this type of cellular tumor has a high incidence of recrudescence. Your veterinarian will monitor the area in follow up visits, and if the hemangiopericytoma should recur, you doctor will explain the options to you so that you can make the treatment decision that is most appropriate for your dog.

In some patients amputation of the affected limb is an option, as this will remove the entire affected area. Because this type of tumor usually remains local and does not spread out in the body, this can be a very effective method for resolving the issue. Another method is to remove the growth again. This method, along with radiotherapy, may be effective, especially for those patients in which complete removal of mass is not possible. The drawback is that if the tumor should return yet again, it will be more deeply rooted in the tissue, as each recurrence becomes more invasive than the last. The last method is to take no action at all. This may be the appropriate response, especially if your dog is older. The tumor grows at a slow rate and does not affect the animal's health until it has grown to a size where it is affecting the organs and/or limbs. Conversely, this may not be the appropriate response if your dog is young.

Living and Management

The overall survival time largely depends upon the nature of the tumor and the aggressiveness with which surgery and treatment are conducted. A cure is possible in dogs that have undergone early and aggressive surgical resection of the tumor. Because recurrence of hemangiopericytoma is common, you will need to take your dog for regular follow up checkups or radiotherapy treatments. Your veterinarian will set up a schedule for progress evaluation visits.

Your veterinarian will prescribe post-surgery pain killers for your dog to help make it more comfortable. Use pain medications with caution; one of the most preventable accidents with pets is due to overdose of medication. Cage rest is recommended after surgery. A quite area set aside, away from household traffic, active children and other pets will help your dog to recover. Also, setting the food dishes close by to where your dog is convalescing will allow your dog some independence. Outdoor trips, for when your dog needs to relieve itself, should be unhurried and close to home. Assist your dog as much as possible. If necessary, you might consider setting up a temporary area for your dog to relieve itself more comfortably, but consult your veterinarian first, as you may then need to break your dog from the new habit of relieving itself indoors.

Keep in mind that you should not leave the dog alone for extended periods of time. Affection is a great help for recovery, and you will need to make sure that the dog is not laying in the same position for long. In case of limb amputation, most dogs recover well, learning to compensate for the lost limb.

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