Fatty Tissue Tumors (Lipomas) in Dogs

Fatty tissue tumors are common in dogs, and their cause is not well understood. There are different types of fatty (adipose) tissue tumors, which vary slightly in characterization.

Lipomas are the most common type of adipose tumor. Most commonly developing under the skin, a lipoma is a collection of fat cells that are replicating at a faster rate than normal, forming a soft lump. These lumps often shrink if a dog loses weight, although they are unlikely to disappear completely. Lipomas are benign, and unlikely to seriously impact a pet’s health.

Diffuse Lipomatosis has only been identified in dachshunds. Unlike a lipoma, which is a definable lump, diffuse lipomatosis is a widespread proliferation of fat cells in multiple areas throughout the body, with no distinguishable beginning or end to the proliferation. These masses are most common around the neck or trunk area.

Infiltrative Lipomas are benign, however they behave similarly to malignant cancers as they spread into or through adjoining tissues. An infiltrative lipoma may begin in fatty tissue, but spread into muscle or skeletal tissues as it develops.

Liposarcomas are a malignant growth of fat cells. Unlike lipomas, they can be soft or firm, and may excrete a mucus-like fluid if the skin breaks. These tumors frequently invade surrounding tissue, and may metastasize to lymph nodes or other organs.

Veterinary assistance is essential to properly identify and treat any masses, and any dog presenting with symptoms requires prompt medical intervention.

The severity of fatty tissue tumors depends on the type of tumor, the location, and its size.

Lipomas rarely impact overall health, although they may cause discomfort if they grow in an inconvenient place, such as over a joint. Other forms of adipose tumors are malignant and can spread through adjacent tissue, potentially causing damage to nerves, vessels, and other structures.

A tumor growing around a joint or other high-motion areas may cause discomfort, manifesting as limping or excessive grooming of an affected area. In some cases, fatty tumors can become extremely large and heavy, and may make normal daily activities difficult.

Since the underlying cause of lipomas is not well understood, it is difficult to identify specific risk factors or predilections. There is some evidence that lipomas may be associated with obesity in dogs.

The underlying cause of lipomas is not well understood at this time.

These tumors are soft, squishy, and can grow to be quite large. Most often, these masses have well-defined edges that can be felt under the skin.

Diagnostics include:

• Physical Examination
• Diagnostic imaging if invasion into other tissues is suspected
• Fine needle aspiration
• Tissue biopsy

Some cases of fatty tissue tumors require no treatment. If treatment is required, most adipose tumors are treated with surgical excision. Complete removal of the mass is more difficult in cases of malignant tumors due to infiltration of surrounding tissues, which may lead to amputation or removal of extensive areas of skin in severe cases. Malignant tumors may also be treated with radiation therapy.

Prognosis is variable, depending on the type of adipose tumor. Lipomas are the most common form of fatty tumor, and have an excellent prognosis. Diffuse lipomatosis, infiltrative lipomas, and liposarcomas are more difficult to treat, and may recur.

Since the underlying cause is not well understood, it is difficult to speculate on effective prevention. Appropriate weight control may reduce the likelihood of developing adipose tumors. Staying up to date with routine veterinary care helps identify tumors early, which maximizes long term outcomes.

Lipomas are common in dogs. Some breeds are predisposed to fatty tissue tumors, as are older dogs and overweight dogs.

• Benign neglect
• Surgical removal
• Radiation therapy
• Amputation