Fatty Tissue Tumor (Benign) in Dogs

Infiltrative Lipoma in Dogs

Infiltrative lipoma is a variant tumor that does not metastasize (spread), but which is known to infiltrate the soft tissues, notably the muscles. It is an invasive, benign tumor composed of fatty tissue, and while it is known mainly for its penetration into muscular tissue, it is also commonly found in the fasciae (the soft tissue component of the connective tissue system), tendons, nerves, blood vessels, salivary glands, lymph nodes, joint capsules, and occasionally the bones. Muscle infiltration is often so extensive that surgery cannot be performed without severe consequences.

Infiltrative lipoma occurs much less frequently than does lipoma. When it does occur, it is usually in middle-aged dogs, and it tends to affect females more so than males. Labrador retrievers are suspected to be at higher risk.

Symptoms and Types

• Large, soft tissue mass
• Muscle swelling
• Infiltration of pelvic, thigh, shoulder, chest, and lateral cervical musculature (side of neck)

Causes

Diagnosis

You will need to give a thorough history of your dog’s health and onset of symptoms. Your veterinarian will use X-ray imaging to reveal the fat dense tissue between the soft tissue dense structures, and a computed tomography (CT) scan will help to discriminate the nature of the tumor so that your doctor can plan what type of radiation treatment would be best. However, differentiating normal fat from an infiltrative lipoma can be very complicated and problematic.

A sample of tumor cells may be taken by needle aspirate for laboratory analysis, and this may help your doctor to distinguish between normal adipose (fatty) tissue and a lipoma tumor. Lipoma tumors do have a distinctive feature in that they infiltrate muscles, so your doctor may be able to make a form diagnosis based on their behavior within the muscular structure.