Lumps and Bumps: Lipomas (fatty tumors)
Understanding Your Pet's Medical Diagnosis

By Janet Tobiassen Crosby D.V.M. and Theresa A. Fuess Ph.D.

What is a Lipoma?

A Lipoma is a benign fatty lump. They are very common in middle-aged and older dogs. Overweight females are especially prone to developing them. Certain dog breeds may be at greater risk, including, but not limited to, Doberman Pinschers, Miniature Schnauzers, Labrador Retrievers and mixed breeds.

Lipomas are usually just under the skin, but they can be locally invasive, meaning they are meshed with muscle and connective tissue. Lipomas can also have additional blood or connective tissue as part of the growth. These growths can appear anywhere on the body but are most frequently located on the belly (mid-chest and lower) and upper legs.

What causes Lipomas?

In most cases dogs develop Lipomas as a natural result of the aging process. In the same way that some humans develop wrinkles as they age, some dogs will develop Lipomas as they grow older.

What are the signs of Lipomas?

While petting and grooming, dog owners should make a habit of looking for irregularities (lumps and bumps) on their pets, paying close attention to the most common sites for tumors. Pet owners should also be aware of changes in their dog's attitude and appetite.

Are Lipomas ever malignant?

Yes, although rare, there is a fatty tumor called a liposarcoma, and this is malignant. Metastasis is rare, but due to their infiltrative nature, they are difficult to fully remove and recurrence is common.

How are Lipomas diagnosed?

Any and all lumps should be checked by your veterinarian. Your vet will assess the location, duration, firmness and size. A needle aspirate may also be taken to look at what type of cells makes up the lump. This is the easiest way for your vet to determine if a lump is benign or malignant.

What is a needle aspirate?

A needle aspirate is when a sterile needle is inserted into the lump and the plunger is withdrawn, providing suction to collect cells from the lump. This is not painful, and not usually noticed by most dogs. Your vet will then place the collected cells on a microscope slide, stain them, and take a look at them in the microscope. The cells, when examined this way, will look like normal healthy cells if the tumor is benign or will appear abnormal if the tumor is malignant. If the cells do not clearly fit either the benign or malignant categories, then your vet may recommend removing the lump.

How are Lipomas treated?

Many lumps, benign or malignant, can be cured/treated with surgery. If the lump is a benign fatty tumor, and surgery is not necessary, most vets will recommend a "watch and wait" approach.

What is the best way to "watch" a lump?

After your vet has assessed the lump and you are officially "watching it" for any changes, it is recommended that you:

In addition to monitoring, the lump should be examined yearly by your vet, or sooner if changes occur before that point.

What is the prognosis for animals with Lipomas?

Many animals have lumps (fatty tumors) all their lives and they remain benign. However, if a lump is malignant, your dog has a better prognosis if treated early. Options for treatment will be greater and your dog will have a better chance of recovery.

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