Lipoma
Classification and external resources
Lipoma on forearm
ICD-10	D17 (ILDS D17.910)
ICD-9	214
ICD-O:	M8850/0
DiseasesDB	7493
MedlinePlus	003279
eMedicine	med/2720 derm/242
MeSH	D008067

A lipoma is a benign tumor composed of adipose tissue. It is the most common form of soft tissue tumor.^[1] Lipomas are soft to the touch, usually movable, 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 claim that malignant transformation can occur,^[2] while others say that this has yet to be convincingly documented.^[3]

Types[link]

Lipoma removed from human torso

Lipoma of the breast

There are several subtypes of lipoma^[4]:624-5:

• Angiolipoleiomyoma is an acquired, solitary, asymptomatic acral nodule, characterized histologically by well-circumscribed subcutaneous tumors composed of smooth muscle cells, blood vessels, connective tissue, and fat.^[4]:627

• Angiolipoma is a painful subcutaneous nodule, having all other features of a typical lipoma.^[4]:624[5]

• Chondroid lipomas are deep-seated, firm, yellow tumors that characteristically occur on the legs of women.^[4]:625

• Corpus callosum lipoma is a rare congenital brain condition which may or may not present with symptoms.^[6] This occurs in the corpus callosum , also known as the colossal commissure, which is a wide, flat bundle of neural fibers beneath the cortex in the human brain. Lipomas are usually relatively small with diameters of about 1–3 cm,^[7] 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 kg.^[8][9]

• Hibernoma is a lipoma of brown fat.

• Intradermal spindle cell lipoma is distinct in that it most commonly affects women, and has a wide distribution, occurring with relatively equal frequency on the head and neck, trunk, and upper and lower extremities.^[4]:625[5]

• Neural fibrolipoma is an overgrowth of fibro-fatty tissue along a nerve trunk that often leads to nerve compression.^[4]:625

• Pleomorphic lipomas, like spindle-cell lipomas, occur for the most part on the backs and necks of elderly men, and are characterized by floret giant cells with overlapping nuclei.^[4]:625

• Spindle-cell lipoma is an asymptomatic, slow-growing subcutaneous tumor that has a predilection for the posterior back, neck, and shoulders of older men.^[4]:625

• Superficial subcutaneous lipoma, the most common type of lipoma, lies just below the surface of the skin.^[3] Most occur on the trunk, thighs and the forearms, although they may be found anywhere in the body where fat is located.

Prevalence[link]

Approximately one percent of the general population has a lipoma.^[3] These tumors can occur at any age, but are most common in middle age, often appearing in people from 40 to 60 years old.^[10] Cutaneous lipomas are rare in children, but these tumors can occur as part of the inherited disease Bannayan-Zonana syndrome.^[11][12]

Causes[link]

The tendency to develop a lipoma is not necessarily hereditary although hereditary conditions, such as familial multiple lipomatosis, may include lipoma development.^[13][14] Genetic studies in mice 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.^[15]

Cases have been reported where minor injuries are alleged to have triggered the growth of a lipoma, called "post-traumatic lipomas."^[16] However, the link between trauma and the development of lipomas is controversial.^[17]

Treatment[link]

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.^[3] This last point can be important as the actual identity of a "bump" is not known until after it is removed and professionally examined.

Lipomas are normally removed by simple excision.^[10] The removal can often be done under local anaesthetic, and take less than 30 minutes.^[18] This cures the majority of cases, with about 1-2% of lipomas recurring after excision.^[19] 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.^[20]

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.^[10][21]

• Resection of an intermuscular lipoma in the elbow region
• 

  X-ray of the lipoma.

• 

  Intraoperative photo.

• 

  The operating field after removal of the lipoma. Arrow marks the median nerve which was compressed by the lipoma.

• 

  The resected lipoma
  (8 cm × 6 cm × 3 cm)

Prognosis[link]

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.^[22][23] Malignant transformation of lipomas into liposarcomas is very rare and most liposarcomas are not produced from pre-existing benign lesions,^[19] although a few cases of malignant transformation have been described for bone and kidney lipomas.^[24][25] It is possible these few reported cases were well-differentiated liposarcomas in which the subtle malignant characteristics were missed when the tumour was first examined.^[26] Deep lipomas have a greater tendency to recur than superficial lipomas, because complete surgical removal of deep lipomas is not always possible.^[26][27]

In veterinary medicine[link]

Lipomas occur in many animals, but are most common in older dogs, particularly older Labrador Retrievers, Doberman Pinschers and Miniature Schnauzers.^[28] Overweight female dogs are especially prone to developing these tumors and most older or overweight dogs have at least one lipoma.^[29][30] In dogs, lipomas usually occur in the trunk or upper limbs.^[28] Lipomas are also found less commonly in cattle and horses, and rarely in cats and pigs.^[30][31] However, a pedunculated lipoma can cause entrapment and torsion of the intestine in horses, causing necrosis, colic, and possibly death. The intestine becomes wound around the stalk of the lipoma and loses blood supply.^[32]

Other conditions involving lipoma[link]

Lipomatosis is a hereditary condition where multiple lipomas are 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, post-menopausal women.^[33]

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.^{[citation needed]}

See also[link]

• List of cutaneous conditions

References[link]

External links[link]

Images and video[link]

• Illustration from University of Connecticut Health Center
• Esophageal Lipomatosis MedPix Images from Uniformed Services University of the Health Sciences
• Lipoma images from DermAtlas
• humpath #2626