Definitions

lipoma

lipoma

[li-poh-muh, lahy-]
lipoma: see neoplasm.

A lipoma is a benign tumor composed of fatty tissue. These are the most common form of soft tissue tumor. Lipomas are soft to the touch, usually moveable, and are generally painless. Many lipomas are small (under one centimeter diameter) but can enlarge to sizes greater than six centimeters. Lipomas are commonly found in adults from 40 to 60 years of age, but can also be found in children. Some sources say that malignant transformation can occur, while others claim that this has yet to be convincingly documented.

Types

Types include:

  • Superficial subcutaneous
  • Intramuscular
  • Spindle cell
  • Angiolipoma
  • Benign lipoblastoma
  • Lipoma of tendon sheath, nerves, synovium or other

The most common type is the "superficial subcutaneous lipoma", i.e. just below the surface of the skin. Most occur on the trunk, thighs and the forearms, although they may be found anywhere in the body where fat is located.

Lipoma of the corpus callosum is a rare congenital condition which may or may not present with symptoms. Lipomas are usually relatively small with diameters of about 1 - 3 centimeters, but in rare cases they can grow over several years into "giant lipomas" that are 10-20 cm across and weigh up to 4-5 kilograms.

Prevalence

Approximately one percent of the general population has a lipoma. These tumors can occur at any age, but are most common in middle age, often appearing in people from 40 to 60 years old. Cutaneous lipomas are rare in children, but these tumors can occur as part of the inherited disease Bannayan-Zonana syndrome.

Causes

The tendency to develop a lipoma is not necessarily hereditary although hereditary conditions, such as familial multiple lipomatosis, may include lipoma development. Genetic studies in mice from the laboratory of Santa J. Ono have shown a correlation between the HMG I-C gene (previously identified as a gene related to obesity) and lipoma development. These studies support prior epidemiologic data in humans showing a correlation between HMG I-C and mesenchymal tumors.

Cases have been reported where minor injuries are alleged to have triggered the growth of a lipoma, called "posttraumatic lipomas". However, the link between trauma and the development of lipomas is controversial.

Treatment

Usually, treatment of a lipoma is not necessary, unless the tumor becomes painful or restricts movement. They are usually removed for cosmetic reasons, if they grow very large, or for histopathology to check that they are not a more dangerous type of tumor such as a liposarcoma.

Lipomas are normally removed by simple excision. This cures the majority of cases, with about 1-2% of lipomas recurring after excision. Liposuction is another option if the lipoma is soft and has a small connective tissue component. Liposuction typically results in less scarring; however, with large lipomas it may fail to remove the entire tumor, which can lead to re-growth.

There are new methods being developed that are supposed to remove the lipomas without scarring. One of them is removal by the use of injection of compounds that trigger lipolysis, such as steroids or phosphatidylcholine. Another method being developed is the use of ultrasound waves to destroy the lipoma. This can be compared with the removal of kidney stones where ultrasound is used to pulverize the stones.

Prognosis

Lipomas are rarely life-threatening and the common subcutaneous lipomas are not a serious condition. Lipomas growing in internal organs can be more dangerous, for example lipomas in the gastrointestinal tract can cause bleeding, ulceration and painful obstructions. Malignant transformation of lipomas into liposarcomas is very rare and most liposarcomas are not produced from pre-existing benign lesions, although a few cases of malignant transformation have been described for bone and kidney lipomas.

In other animals

Lipomas occur in many animals, but are most common in older dogs, particularly older Labrador Retrievers, Doberman Pinschers and Miniature Schnauzers. Obese female dogs are especially prone to developing these tumors and most older or overweight dogs have at least one lipoma. In dogs, lipomas usually occur in the trunk or upper limbs. Lipomas are also found less commonly in cattle and horses, but rarely in cats and pigs.

Other conditions involving lipoma

Lipomatosis is a hereditary condition where multiple lipomas present on the body.

Adiposis dolorosa (Dercum disease), is a rare condition involving multiple painful lipomas, swelling, and fatigue. It is generally seen in obese, postmenopausal women.

Benign symmetric lipomatosis (Madelung disease) is another condition involving lipomatosis. It nearly always appears in middle-aged males after many years of alcoholism, although non-alcoholics and females can also be affected.

References

External links

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