The lipoma is a benign tumor of the adipocytes. These tumors are usually well-differentiated and present as nodular masses in the subcutis. They are common findings in dogs, especially in the aged, overweight, and female, and are not uncommon in horses and cattle. Lipomas are rare in cats and swine.
A typical lipoma is soft and feels fatty, although lipomas with an associated inflammatory reaction can be fibrous and solid to the touch. The central regions of large lipomas can become necrotic and calcified. The skin can usually be moved freely around a lipoma since the majority does not involve any underlying muscle.
Lipomas are often first discovered by an attentive owner who finds the tumor while grooming the animal. Diagnosis is often made by fine needle aspiration &endash; a good lipoma smear will be slightly yellowish in color, feel greasy to the touch, and will appear highly cellular under the light miroscope. Most lipoma smears end up being sparsely cellular after staining because the fat globules get washed away.
Lipomas are considered benign tumors and they do not usually pose a hazard when restricted to the skin. Exceptions do exist, however, and include cases where the lipoma is so large that it causes damage from pressure or by involving vital structures. This is occasionally seen in the thoracic inlet, where lipomas can compress the esophagus, trachea, and great vessels.
Another potential complication of lipomas is seen in the horse. Lipomas frequently arise from the mesenteric fat where they are attached by thin, fibrous roots. The roots of these tumors can twist around loops of bowel, resulting in infarction and colic.
As is the case with all tumors or strange growths, surgically remove any suspected lipoma and have it biopsied. Most lipomas can be easily removed and pose few complications, but some supposed lipomas may turn out to be cases of liposarcoma, a malignant disease. Definitive treatment of the lipoma is almost always simple excision; even lipomas with dirty margins tend not to recurr.