Papillomas, Lipomas, Cysts, and Basal Cell Tumors in Dogs
Skin tumors are common in dogs. It is often impossible to determine whether a skin tumor is benign or malignant by appearance alone. The only conclusive way to make a diagnosis is by biopsy, a procedure in which tissue or cells are removed by your veterinarian and examined under a microscope by a veterinary pathologist.
For small tumors it is best for your veterinarian to remove the growth and present the entire specimen to the pathologist. For tumors larger than 1 inch (2.5 cm) across, it may be advisable for your veterinarian to obtain a tissue sample by fine needle aspiration. In this procedure, a needle connected to a syringe is inserted into the tumor and cells are obtained by pulling back on the plunger. Alternatively, the vet can use a cutting needle to obtain a core sample. An open biopsy, in which an incision is made, is preferred for suspected sarcomas and tumors that present diagnostic problems for the pathologist.
Skin papillomas are benign wartlike growths that occur on the skin of the body, on the foot pads, and beneath the nails. They are caused by the canine oral papilloma virus and tend to occur in older dogs, especially older Poodles.
Treatment: They do not need to be removed unless they are causing a problem because of their location on the body. Rarely, these will become injured and bleed or get infected. In these cases, removal is recommended.
A hematoma is a blood clot beneath the skin, caused by a blow or contusion. These are not cancers. Large ones may need to be drained. Ear flap hematomas require special attention (see Swollen Pinna).
Calcifying hematomas are hard masses that resemble bone. They tend to occur at fracture sites, and may be found as a bump on the skull of a tall dog who strikes her head on the underside of the dining room table.
Treatment: Calcifying hematomas do not need be removed but may have to be biopsied if there is a question of bone tumor. They are difficult to treat and often recur.
Epidermal Inclusion Cysts (Sebaceous Cysts)
Epidermal inclusion cysts, also called sebaceous cysts, are common surface tumors found anywhere on the body. Kerry Blue Terriers, Schnauzers, Poodles, and spaniels are most often affected. Epidermal inclusion cysts begin when dry secretions block hair follicles, causing an accumulation of hair and sebum (a cheesy material), and the subsequent formation of a cyst.
These cysts produce a dome-shaped swelling up to an inch or more in size beneath the skin, though most are smaller. They can become infected and may need to be surgically drained. This sometimes leads to a cure.
Treatment: Surgical excision is the treatment of choice, although it is not always required.
A lipoma is a benign growth made up of mature fat cells interlaced with fibrous connective tissue. Lipomas are common in overweight dogs, especially females. A lipoma can be recognized by its oblong or round appearance and smooth, soft, fatlike consistency. Lipomas grow slowly and may get to be several inches in diameter. They are not painful. Rarely, what appears to be a lipoma is a malignant variant called a liposarcoma.
Treatment: Surgical removal is necessary if the lipoma is interfering with the dog's mobility, is growing rapidly, or is cosmetically bothersome. The tumor should be biopsied if there is any question about the diagnosis.
Histiocytomas are rapidly growing tumors found in dogs 1 to 3 years of age. They occur anywhere on the body. These benign tumors are dome-shaped, raised, hairless surface growths that are not painful. Because of their appearance, they are often called button tumors. These benign growths are more common on shorthaired dogs.
Treatment: Most histiocytomas disappear spontaneously within one to two months. Those that persist should be removed for diagnosis.
These are common benign tumors found more often in older dogs, particularly Boston Terriers, Poodles, and Cocker Spaniels. The average age of dogs with sebaceous adenomas is 9 to 10 years.
Sebaceous adenomas arise from the oil-producing sebaceous glands in the skin. They tend to occur on the eyelids and limbs. They may be single or multiple, usually are less than 1 inch (25 cm) across, and appear as smooth, lobulated growths on a narrow base or stem. The surface of the tumor is hairless and may be ulcerated.
Occasionally, a sebaceous adenoma becomes malignant (becoming a sebaceous adenocarcinoma). Suspect malignancy if the tumor is larger than 1 inch, has an ulcerated surface, and is growing rapidly.
Treatment: Small tumors do not need to be removed unless they are causing a problem. Large adenomas should be removed.
Basal Cell Tumors
This is a common tumor usually found on the head and neck in dogs over 7 years of age. It appears as a firm, solitary nodule with distinct borders that sets it apart from the surrounding skin. The tumor may have been present for months or years. Cocker Spaniels appear to be at increased risk.
A small percent of basal cell tumors are malignant, becoming basal cell carcinomas.
Treatment: Basal cell tumors should be removed by wide surgical excision.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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