Lipoma. What is it?
A lipoma is a benign tumor composed of adipose tissue (body fat). It is the most common benign form of soft tissue tumor. 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 younger adults and children. Some sources claim that malignant transformation can occur, while others say this has yet to be convincingly documented.
There are many subtypes of lipomas:
– Adenolipomas are lipomas associated with eccrine sweat glands.
– Angiolipoleiomyomas are acquired, solitary, asymptomatic acral nodules, characterized histologically by well-circumscribed subcutaneous tumors composed of smooth muscle cells, blood vessels, connective tissue, and fat.
– Angiolipomas painful subcutaneous nodules having all other features of a typical lipoma.
– Cerebellar pontine angle and internal auditory canal lipomas
– Chondroid lipomas are deep-seated, firm, yellow tumors that characteristically occur on the legs of women.
– Corpus callosum lipoma is a rare congenital brain condition that may or may not present with symptoms. 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.
– Hibernomas are lipoma of brown fat.
– Intradermal spindle cell lipomas are distinct in that they most commonly affect women and have a wide distribution, occurring with relatively equal frequency on the head and neck, trunk, and upper and lower extremities.
– Neural fibrolipomas are overgrowths of fibro-fatty tissue along a nerve trunk, which often leads to nerve compression.
– 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.
– Spindle-cell lipomas are asymptomatic, slow-growing subcutaneous tumors that have a predilection for the posterior back, neck, and shoulders of older men.
– Superficial subcutaneous lipomas, the most common type of lipoma, lie just below the surface of the skin. Most occur on the trunk, thigh, and forearm, although they may be found anywhere in the body where fat is located.
Don’t forget to read Lipoma Treatment and Prognosis. Lipoma in Veterinary Medicine
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.
Lipomas are usually relatively small with diameters of about 1–3 cm, 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.
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 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 “post-traumatic lipomas.” However, the link between trauma and the development of lipomas is controversial.