A lipoma is a benign (noncancerous) tumor made up of fat tissue. The typical lipoma is a small, soft, rubbery lump located just beneath the skin. They are usually painless and are most often found on the upper back, shoulders, arms, buttocks, and upper thighs. Less commonly, these tumors can be found in deeper tissue of the thigh, shoulder, or calf.
Although lipomas can occur at any age, they most often appear between the ages of 40 and 60 years. They are the most common soft tissue tumor found in adults, and occur slightly more often in men than in women. It is possible to have more than one lipoma.
Lipomas typically do not change after they form, and have very little potential for becoming cancerous. They often require no treatment other than observation. However, if a lipoma is painful or continues to grow larger, it can be removed with a simple excision procedure.
While all lipomas are made up of fat, there are sub-types based on the way they appear under the microscope. Some varieties include:
- Conventional lipoma (common, mature white fat)
- Hibernoma (brown fat instead of the usual white fat)
- Fibrolipoma (fat plus fibrous tissue)
- Angiolipoma (fat plus a large amount of blood vessels)
- Myelolipoma (fat plus tissue that makes blood cells)
- Spindle cell lipoma (fat with cells that look like rods)
- Pleomorphic lipoma (fat with cells of all different shapes and sizes)
- Atypical lipoma (deeper fat with a larger number of cells)
The cause of lipomas is not completely understood. Some sub-types appear to have a genetic defect (conventional lipomas, spindle cell lipomas, pleomorphic lipomas), and may be inherited from family members.
There has been no proven connection between the development of lipomas and any particular occupation or exposure to chemicals or radiation. Some doctors think that lipomas occur more often in inactive people.
Lipomas are usually roundish masses that feel soft and rubbery. The lipomas just under the skin can be moved with just gentle pushing. Lipomas do not typically hurt, although some of the subtypes can be painful, such as angiolipoma.
It often takes longer to notice lipomas that are in deeper tissue, and these tumors can be quite large when they are actually discovered. Deeper lipomas also tend to be less mobile.
Medical History and Physical Examination
Before a physical examination, your doctor will talk with you about your general health, as well as your current condition. He or she will want to get a good history of the problem from your perspective, particularly how long the mass has been there and what symptoms —such as pain —that are associated with it.
During the physical examination, your doctor will feel the mass, checking its size and consistency, as well as its mobility. He or she will also examine the skin overlying the mass, looking for any changes.
Although doctors can usually diagnose lipomas based on history and physical examination alone, imaging tests can be helpful.
X-rays. Although these tests create clear pictures of dense structures like bone, plain x-rays can show a prominent shadow caused by a soft tissue tumor.
Computed tomography (CT) scans. These scans are more detailed than x-rays and will often show a fatty mass to confirm the diagnosis of lipoma.
Magnetic resonance imaging (MRI) scans. The best information for diagnosing lipoma comes from an MRI scan, which can create better images of soft tissues like a lipoma. MRI scanning will show a fatty mass from all perspectives. Oftentimes, doctors can make the diagnosis of lipoma based on MRI imaging alone, and a biopsy is not required.
Biopsy. A biopsy is sometimes necessary to confirm the diagnosis of lipoma. In a biopsy, a tissue sample of the tumor is taken and examined under a microscope. Your doctor may give you a local anesthetic to numb the area and take a sample using a needle. Biopsies can also be performed as a small operation.
In most cases of lipoma, a biopsy is not necessary to confirm the diagnosis. After the lipoma is removed, a biopsy will be done on a sample of the tissue.
Under a microscope, lipomas often have a classic appearance with abundant mature fat cells. Sometimes there can be a small amount of other cell types, too, such as cartilage or bone.
Liposarcoma. During the diagnosis phase, your doctor will work to differentiate a lipoma from a more aggressive form of fatty tumor called liposarcoma. Liposarcomas are cancerous. The symptoms of liposarcoma vary from those of lipoma. Liposarcomas typically grow quickly, are often painful, and are not as moveable as lipomas.
People with lipomas are not more likely to develop liposarcomas in the future. The exception is people with atypical lipomas. This lipoma sub-type can turn into a liposarcoma, but this is extremely rare.
Because lipomas are benign tumors, no treatment may be an option, depending on your symptoms. If you choose no treatment, it is very important that you see your doctor for regular visits to monitor any changes in the tumor.
The only treatment that will completely remove a lipoma is a simple surgical procedure called excision.
Procedure. In this procedure, a local anesthetic is typically injected around the tumor to numb the area. Large lipomas or those that are deep may require regional anesthesia or general anesthesia. Regional anesthesia numbs a large area by injecting numbing medicine into specific nerves. General anesthesia puts you to sleep.
After the anesthesia is given, your doctor will make an incision in your skin and cut the tumor out.
Recovery. You should be able to go home soon after the procedure. You will have a few stitches, which your doctor will remove within a couple of weeks.
How long it takes you to return to most daily activities will depend on the size and location of your lipoma. If you have any pain or discomfort, you may want to limit some activity. Your doctor will provide you with specific instructions to guide your recovery.
Recurrence. Lipomas are almost always cured by simple excision. It is unusal for a lipoma to grow back, but if it does recur, excision is again the best treatment option.
There is ongoing research to learn more about the various sub-types of lipomas and why they form in the first place. In the future, there may be specific treatment recommendations for various lipoma sub-types.
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