Lipomas in Dogs

Types of Lipomas

There are 3 main types of lipomas. The most common is the simple lipoma which tends to develop in the subcutaneous (fatty tissue layer) under the skin on the body and limbs. These growths are typically slow-growing, nonpainful, and moveable. Lipomas can also develop in the chest and abdomen or between muscles, but these are less common.

Infiltrative lipomas are locally aggressive and can invade surrounding tissue. These can be soft and mobile, or firm and fixed in their location.

Myelolipomas are lipomas that are made of both fat cells and hematopoietic cells. This type of lipoma tends to develop on the liver, spleen, or adrenal glands. These are also benign tumors.

Clinical Symptoms of Lipomas in Dogs

• Soft, often slightly moveable, nonpainful lump under the skin
• If the lipoma is in the chest, you may notice your dog breathing faster, shallow, or coughing
• Lipomas on the spleen are rare, but they can grow and rupture the splenic capsule leading to internal bleeding. If this occurs, you may notice pale gums, a distended abdomen, rapid breathing, and collapse
• If the lipoma becomes necrotic by outgrowing the blood supply or if the blood supply is disrupted, it can lead to heat, swelling, pain, and infection.
• Lipomas that develop between muscles can lead to pain and difficulty moving the affected limb/region.
• Rarely, lipomas can infiltrate into the nervous system and cause neurologic symptoms

Diagnosing Lipomas in Dogs

All growths should be aspirated and evaluated with cytology to look at the cells obtained. It’s impossible to feel a growth and know for sure what it is. Many other tumors can feel the same, such as subcutaneous mast cell tumors and soft tissue sarcomas.

Cytology by fine needle aspiration (FNA) is the most common test to help diagnose a growth. A small needle is directed into the growth, and cells are removed to evaluate under the microscope. Organized fatty cells are the most common cell seen on cytology if the growth is a lipoma. This test cannot differentiate between simple lipomas, infiltrative lipomas, and normal fat in the body.

If a mass is felt in the abdomen, radiographs or an ultrasound may be recommended to get a better idea of the location, size, and see if the mass is in a location where FNA or biopsy is possible to obtain cells or tissue for testing.

Biopsy and histopathology can get a true diagnosis. This type of test requires a section of the growth to evaluate and often requires sedation or anesthesia. Your vet may do this before removing the entire tumor to ensure it is just a benign growth and nothing more serious. Ideally, all growths that are removed should be submitted for histopathology to obtain a diagnosis and ensure the growth was completely removed.

Treatment Options for Lipomas in Dogs

Since most lipomas are slow-growing and benign, simply monitoring them for any changes is a good option. If the lipoma starts to grow rapidly, changes in texture (soft to firm), or if it becomes painful, it’s time to go back to the vet to get the area re-evaluated. The lipoma may have become necrotic or infected.

If the lipoma is large, near a joint, or interferes with movement, it can be removed surgically. Surgical removal is typically curative. A drain tube may need to be placed to facilitate fluid drainage from the site as it heals post-operatively.

Infiltrative lipomas tend to grow faster and grow around surround tissues, which can be painful. Surgery can be difficult, but as much of the growth as possible should be removed. Following surgery with radiation therapy can help resolve the remaining lipoma.

Lipomas in the chest or abdomen can be removed if they’re causing issues or to reduce the risk of internal bleeding if the tumor ruptures the capsule of the organ they may be invading. Discuss the pros and cons with your vet.

Injecting a steroid directly into a lipoma can lead to a reduction in size, but many often recur 6 months or so after treatment.

Final Thoughts

Lipomas are very common, typically slow-growing, benign tumors in dogs. Dogs can develop multiple lipomas. All new growths should be evaluated and tested by your vet to be sure there is nothing more serious forming. Don’t forget, you can’t diagnose a growth just by feeling it!

Read more:

Warning Signs of Cancer in Dogs

Mast Cell Tumors in Dogs

Hemangiosarcoma in Dogs

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