Lipoma

Lipomas are usually non-cancerous growths, or tumours, caused by abnormal genes in fat cells

Alternative names

fatty tumours, fatty growths, neoplasm

What are lipomas?

Lipomas are a form of benign (non-cancerous) neoplasm (meaning 'new growth') or tumour, made up largely of fat cells. They are usually classified as harmless, as the growth occurs only in the local area and does not spread to other parts of the body, as cancer cells do. A lipoma appears as a lump or bump under the skin, and may be single or multiple.

What causes lipomas?

Cells in the body of the growing foetus normally divide and grow very rapidly. This divide-and-grow pattern continues throughout early childhood and puberty. During adulthood, however, new cells are formed only when they are needed to replace cells that die from injury, old age or disease. Genes (composed of DNA) contained within each cell control the division of cells. However, if these genes become damaged and undergo mutation (change), they may cause the cell to start dividing in an uncontrolled way.

When a fat cell become abnormal, a lipoma or new growth of fatty tissue occurs. The fat cells begin reproducing, producing thousands of copies of themselves. Some research indicates that this is as a result of a genetically acquired abnormality.

The proper function of fat cells is to act as a storage place for fat before it is converted into energy. The fat cells comprising lipoma growth stop performing this function, and instead divert resources from healthy fat cells to fuel the growth of the lump or tumour.

Who gets lipomas and who is at risk?

Lipomas are extremely common, and can occur in people of any age or set of circumstances; however, they are most prevalent in women over the age of 40, and particularly women over the age of 50. They are not nearly as common in men, though they do occur occasionally.

Some evidence indicates that lifestyle may affect the occurrence of lipomas, but most believe that they are caused by a genetic pattern passed on from one generation to the next.

Characteristics and symptoms of lipomas

• A lipoma is typified by the appearance of a soft, movable lump of any size under the skin. The lump usually grows gradually or may stop growing.
• Most lipomas occur in areas of fat under the skin.
• They are surrounded by a thin protein capsule, which demarcates the tumour from the surrounding fatty tissue.
• They generally occur on one side of the body.
• Lipomas usually occur beneath the skin, in the fat of the thighs, back, neck or shoulder.
• Lipomas may also grow in areas that don't contain many fat cells.
• Occasionally, lipomas may appear in the soft tissue of the hands and feet, in the brain, in the heart, within the wall of the digestive tract, inside the muscle tissue or in the spinal cord.
• These benign tumours are not usually painful or itchy, although some kinds of lipoma, which contain blood vessels, muscle or other types of cells, might cause pain.
• They are sometimes associated with a form of obesity, called Dercum's disease, which is common among middle-aged women.
• Abdominal pain, or pain related to organs in the chest, may occur with some kinds of lipoma.

Different kinds and locations of lipomas

The most common kind of lipomas are found in fatty tissue, and are not problematic, but lipomas can also be found in muscles, near organs inside the body, and so on.

Tumours in the mediastinum (the space within the chest between the lungs, where the heart, major blood vessels, trachea and oesophagus are found) can grow very large without causing trouble, but are usually removed to avoid recurrence.

Tumours in the small intestine are very unusual. When they do occur, they cause abdominal pain often resulting from partial blockage in the bowel. Removing the affected areas (resection) is difficult, as the small bowel may be affected in various areas by lipomas.

Spindle cell lipoma occurs mainly in men, when mature fat cells are replaced by collagen – a protein found in the muscle and bone. This results in the formation of spindle cells, which appear on the back or the neck, and are most common among men aged 45-65 years.

Pleomorphic lipoma is also called 'atypical' lipoma. These are similar to spindle cell lipomas, but are made up of much larger cells.

Angiomyolipoma is more common in women than in men. These lipomas occur in the liver or kidney, and are made up of fat, smooth muscle and blood vessels. Although the cells are well demarcated from the healthy cells, angiomyolipoma sometimes extends into organs in the surrounding abdominal cavity. In addition, angiomyolipomas may occur either on their own, or together with other kinds of tumours in the same, or in different organs. They may cause abdominal pain, and are sometimes released in urine.

Lipomas of the spine are very rare, and for some reason occur most commonly in children. These lipomas require complicated surgery and other treatments.

How are lipomas diagnosed?

Doctors will look for the following when diagnosing lipoma clinically:

• soft, movable lumps under the skin
• tumours that are of between one and four centimetres, or larger
• indications that the lipoma is not typical

The lipoma very occasionally exhibits dead cells and signs of bleeding.

Clinical diagnosis might be followed by investigative tests, especially if lipomas are suspected inside the body, or if there is a chance that the lumps may not be benign lipomas, but instead malignant tumours. Tests might include:

• X-rays
• Cat scans (CT, or Computerised Tomography)
• MRI scans (Magnetic Resonance Imaging)

These tests should be followed by a biopsy on the tumour to identify fat-laden cells and confirm the diagnosis.

A family history of lipoma might also support the diagnosis.

Can lipoma be prevented?

Most specialists believe that prevention of lipomas through diet, exercise or lifestyle is not possible, although a few health experts believe that exercise may reduce the risk of their formation by increasing circulation and discouraging fatty deposits, as lipomas seem to be more common among women who are very overweight (Dercum's disease).

How is lipoma treated?

Most lipomas are benign, and do not require treatment. Lipoma is usually treated, if at all, by surgically removing (excising, or resecting) the tumour, or by liposuction, which causes less scarring. A lipoma is only removed when:

• it is so large and unsightly that it is removed for cosmetic reasons.
• it is constricting other organs, or preventing them from working.
• it is in an area where recurrence could be dangerous.
• it is suspected to be a cancerous tumour and must be removed for diagnosis.

In rare cases when lipomas arise inside or near internal body organs, a surgeon may have to perform surgery while the patient is under general anesthetic, which has associated risks.

Radiation therapy, which reduces the size of the tumour, may also be used in cases where surgery is dangerous or impractical because the tumour is inaccessible.

What is the outcome of lipoma?

No treatment, however successful, guarantees that new lipomas will not begin growing in other areas, or that all traces have been removed from the affected area. However, treatment can provide relief from pain and can remove unsightly lumps from under the skin.

Lipomas only result in complications when:

• they grow to enormous sizes,
• are very prevalent, or
• when they are positioned in areas where they might interfere with important bodily functions, such as in the neck, the spinal cord, within the muscle, near organs such as the brain, the heart, the kidneys, or near major arteries.

When to call the doctor

It is important to establish that a suspected lipoma is not a dangerous cancerous growth mistaken for lipoma. If you are not sure of the nature of a lump, always consult a doctor and insist that it be thoroughly investigated.