LIPOMA

THE LIPOCYTE (ALSO CALLED "THE ADIPOCYTE")

Fat is an important resource to our bodies. It is burned aerobically in times of steady exertion and in time of starvation and provides insulation against the cold. Our bodies have a nearly unlimited capacity to store fat, which has unfortunately, led to an epidemic of obesity. Fat is stored within "lipocytes" more commonly referred to as fat cells. These cells consist of a thin cell membrane and nucleus around a large fat storage space called a "vacuole." The normal fat cell can enlarge spectacularly as it stores large amounts of fat.

The "honey-comb" structure represents the walls of a group of fat cells.
The clear contents of the honey-comb are the fat storage areas.
Photo Credit: Wikimedia Commons; Courtesy: Department of Histology, Jagiellonian University Medical College 

HOW DO WE KNOW IT'S A LIPOMA?

The lipoma has a fairly characteristic texture: rubbery and relatively soft; however, it is probably not adequately accurate to make the diagnosis based on simply how a lump feels. A needle aspirate can be easily performed by withdrawing some cells from the mass with a syringe and looking for fat droplets on a microscope slide. This procedure is commonly performed and generally provides adequate results. Of course, if there is any question, the tissue can be biopsied for accuracy.

SHOULD THE LIPOMA BE REMOVED?

In most cases the problem is a cosmetic one. If the mass is unsightly, it can usually be removed provided that the patient has no health problems precluding anesthesia. In some cases, a large lipoma can grow in an inopportune location where it is uncomfortable or where it interferes with movement. In these instances, removing the lipoma is probably a good idea. Often, lipomas are left alone if they do not seem to bother the patient. Surgical removal is usually easy as most lipomas can simply be peeled out of their location.

MALIGNANT LIPOMA?

There is a version of the lipoma which is more infiltrative into other tissues and is more difficult to remove. This type of lipoma does not peel out, is not encapsulated, and does not have obvious margins. There is a 36% recurrence rate for this type of lipoma whereas ordinary lipomas do not generally grow back.

Though it is rare, there is a malignant version of the lipoma called a "liposarcoma." This is also a more infiltrative tumor though it does not generally spread through the body in the way we usually think of malignancy. A wide surgical excision is needed to control this type of fat tumor.

All three forms of lipoma
(the "regular,"  the more infiltrative, and the malignant form)
will look the same when aspirated for fat cells during an office examination.

LOOK ALIKES

There are a couple of malignant tumors that can mimic the rubbery nature of the lipoma. The mast cell tumor is a highly inflammatory and potentially very malignant growth of the skin and subcutaneous tissue. The needle aspirate of a mast cell tumor will look very different from that of a lipoma so, in most cases, these can be distinguished during the initial office evaluation. The hemangioperictyoma is also rubbery like a lipoma and contains enough fat to confound the aspiration examination. In fact, several soft tissue sarcomas can be difficult to distinguish from a lipoma, though in most cases they seem subjectively more deeply rooted and firm. Biopsy may be needed to obtain a definitive answer and plan therapy in the event that a rubbery mass somehow doesn't seem quite typical for a lipoma.

If you notice a lump on your pet, it is probably prudent to show your veterinarian. Most lumps require some sort of tissue sampling for diagnosis, though there are a few that can be identified by visual inspection by the doctor. Since there is a potential for any lump to represent as serious growth, it is important to take lumps and growths seriously have the doctor check them out.

Page posted: 12/14/2011
Page last updated: 1/3/2020
Page last reviewed: 11/14/2021