What Causes Lipoma Lumps?/Lipoma is defined as soft masses of adipose (fat) cells which are often encapsulated by a thin layer of fibrous tissue? Clinically, they often present in the cephalic part of the body, specifically in the head, neck, shoulders, and backs of patients, although they can less commonly be seen elsewhere, for example, the thighs. The tumors typically lie in the subcutaneous tissues of patients. The masses are often benign, and while the age of onset can vary, they most often develop between the age of 40 and 60. There is usually no reason for treatment, as they pose no threat to the patient, unless they are uncomfortable, due to being located on joints or if they are rapidly growing, which is uncommon, as the typical lipoma growth is slow.
A lipoma is a benign tumor made of fat tissue.[rx] They are generally soft to the touch, movable, and painless.[rx] They usually occur just under the skin, but occasionally may be deeper.[rx] Most are less than 5 cm in size.[rx] Common locations include the upper back, shoulders, and abdomen.[rx] A few people have a number of lipomas.[rx]
Types of Lipoma
The many subtypes of lipomas include:[rx]
- 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.[rx]
- Angiolipomas are painful subcutaneous nodules having all other features of a typical lipoma.[rx][rx]
- Cerebellar pontine angle and internal auditory canal lipomas[rx]
- Chondroid lipomas are deep-seated, firm, yellow tumors that characteristically occur on the legs of women.[rx]
- Corpus callosum lipoma is a rare congenital brain condition that may or may not present with symptoms.[rx] 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 lipomas 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.[rx][rx]
- Neural fibrolipomas are overgrowths of fibro-fatty tissue along a nerve trunk, which often leads to nerve compression.[rx]
- 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.[rx]
- Spindle-cell lipomas are asymptomatic, slow-growing, subcutaneous tumors that have a predilection for the posterior back, neck, and shoulders of older men.[rx]
- Superficial subcutaneous lipomas, the most common type of lipoma, lie just below the surface of the skin.[rx] Most occur on the trunk, thigh, and forearm, although they may be found anywhere in the body where fat is located.
Multiple lipomas can be a manifestation of the following syndromes
Proteus syndrome – due to activating mutations in AKT1 oncogene (or occasionally PTEN mutations). It consists of multiple lipomas, epidermal nevi, hemangiomas, palmoplantar cerebriform connective tissue nevi, hyperostoses of the epiphyses and skull, and scoliosis.
Dercum disease (adiposis dolorosa) – consists of multiple painful lipomas on the trunk and extremities which often have overlying paresthesias of the skin. It often affects postmenopausal women who suffer from psychiatric disorders such as depression.
Familial multiple lipomatosis– patients typically present in the third decade with hundreds of discrete, encapsulated, noninfiltrating lipomas. It can be inherited in an autosomal dominant fashion.
Benign symmetric lipomatosis (Madelung disease) – involves diffuse, infiltrative, symmetric painless lipomatous growths affecting the head, neck and shoulder region. Middle-aged alcoholic men are usually affected. Mutations in mitochondrial tRNA lysine gene have been identified in some affected patients.
Gardner syndrome – is due to autosomal dominant mutations in the adenomatous polyposis coli (APC) gene. Nearly all patients develop adenocarcinomas of the GI tract. Cutaneous changes include multiple lipomas, epidermoid cysts, or fibromas. Other associated findings include congenital hypertrophy of retinal pigment epithelium (CHRPE), osteomas of the skull, mandible and maxilla, supernumerary teeth, and various malignancies including papillary thyroid carcinomas, adrenal adenomas, and hepatoblastomas.
Multiple endocrine neoplasia (MEN) type 1 – is due to autosomal dominant mutations in MEN1. It consists of the pituitary, parathyroid, and pancreatic tumors. Cutaneous changes include multiple lipomas (which may also occur in visceral sites), collagenomas, angiofibroma, and cafe au lait macules.
Cowden syndrome – is due to mutations in PTEN and is associated with multiple lipomas, facial trichilemmomas, oral papillomas, punctate palmoplantar keratoses, and a variety of malignancies including breast adenocarcinoma, thyroid follicular carcinoma, endometrial carcinomas, and hamartomatous polyps of the gastrointestinal tract.
Bannayan-Riley-Ruvalcaba syndrome (BRRS) – is also due to PTEN mutations and may represent a pediatric form of Cowden syndrome. Clinical findings include multiple lipomas, genital lentigines, intestinal hamartomas, macrocephaly, and mental retardation.
Where Does a Lipoma Develop?
A lipoma can grow anywhere on the body, but it most often occurs under the skin of these areas:
- Upper back
- Upper thighs
Causes of Lipomas
The tendency to develop a lipoma is not necessarily hereditary, although hereditary conditions such as familial multiple lipomatosis might include lipoma development.[rx][rx] 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.[rx] Cases have been reported where minor injuries are alleged to have triggered the growth of a lipoma, called a “post-traumatic lipoma”.[rx] However, the link between trauma and the development of lipomas is controversial.[rx]
Lipomas can occur more frequently in people with specific medical conditions, such as
- Gardner’s syndrome
- Cowden syndrome
- Madelung’s disease
- adiposis dolorosa
Researchers have also suggested that some lipomas may result from an injury that involves a substantial impact on the area.
Symptoms of Lipoma
A person with a lipoma will typically feel a soft, oval-shaped lump just beneath the skin. Lipomas are usually painless unless they affect joints, organs, nerves, or blood vessels. In most cases, they do not cause other symptoms.
Lipomas can occur anywhere in the body such as:
- Under the skin – especially in the neck, shoulders, back, abdomen, arms, and thighs.
- Soft and doughy to the touch – moves easily with slight finger pressure.
- Generally small – typically less than 2 inches (5 centimeters) in diameter, but they can grow.
- Sometimes painful – Lipomas can be painful when they grow and press on nearby nerves or if they contain many blood vessels.
- Exceptions – some lipomas can be deeper and larger than the usual lipomas.
- Situated just under the skin – They commonly occur in the neck, shoulders, back, abdomen, arms, and thighs.
- Most lipomas – don’t cause any pain or other symptoms but this depends on where in the body it is. If a lipoma is deeper inside your body, you won’t be able to see or feel it but it might press on other organs or nerves.
The following factors may increase the risk of developing a lipoma
- Age between 40 and 60 years old – Lipomas can occur at any age but they’re most common in this age group and are rare in children.
- Having certain other disorders – People with other disorders like adiposis dolorosa, Cowden syndrome and Gardner’s syndrome have an increased risk of multiple lipomas.
- Genetics – Lipomas tend to run in families.
Diagnosis of Lipoma
The doctor will perform the following to diagnose a lipoma
- A physical examination
- 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, such as a lipoma.
An ultrasound of the mass should show that the lipoma – or adipose mass is deeper than the surrounding fatty tissue, as well as, exhibiting dissimilar features as compared to the healthy/normal adipose tissue present
A biopsy (and subsequent analysis of a tissue sample) – is not systematically done in routine practice as the diagnosis is generally made clinically, and since it may be difficult to distinguish lipomas from healthy adipose tissue, histologically speaking
- Shave biopsy – A doctor uses a tool similar to a razor to remove a small section of the top layers of skin (epidermis and a portion of the dermis).
- Punch biopsy – A doctor uses a circular tool to remove a small section of skin including deeper layers (epidermis, dermis and superficial fat).
- Excisional biopsy – A doctor uses a small knife (scalpel) to remove an entire lump or an area of abnormal skin, including a portion of normal skin down to or through the fatty layer of skin. If the lipoma is large and has unusual features or appears to be deeper than the fatty tissue
- Computerized 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 lipomas 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.
It is unusual for a lipoma to be cancerous when it is called a liposarcoma. Liposarcomas are cancerous tumors in fatty tissues which grow rapidly, don’t easily move under the skin and are usually painful. A biopsy, MRI or CT scan is typically done if the doctor suspects liposarcoma.
Treatment of Lipoma
The techniques used for such include, intralesional transcutaneous sodium deoxycholate (associated or not to phosphatidylcholine) injections, intralesional steroids combined with isoproterenol (a beta-2 adrenergic agonist) injections, liposuction of the tumor, or surgical excision. This latter is likely the most effective method to prevent them from reoccurring, though the encapsulation must also be removed for the most effective treatment and to decrease the risk of reoccurrence. If the decision is made to excise lipomas, then it should be done while the lesions are smaller rather than after they grow larger to reduce the risk of these encroaching on joints, nerves, and blood vessels, thus making the excision more difficult and invasive.
Lipomas usually do not require treatment. However, the doctor will recommend removal of the lipoma only if the lipoma is painful or is growing. Lipoma treatments include:
- Surgical removal – Most lipomas are removed surgically by cutting them out. Relapse after removal is uncommon. Possible side effects are scarring and bruising.
- Steroid injections – This treatment shrinks the lipoma but usually doesn’t eliminate it. The use and potential of injections before surgical removal is still being studied.
- Liposuction – In this treatment, a needle and a large syringe are used to remove the fatty lump.
- Lipomas are normally removed – by simple excision.[rx] The removal can often be done under local anesthetic and takes less than 30 minutes. This cures the great majority of cases, with about 1–2% of lipomas recurring after excision.[rx] 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 regrowth.[rx]
New methods under development are supposed to remove the lipomas without scarring. One is removal by injecting compounds that trigger lipolyses, such as steroids or phosphatidylcholine.[rx][rx]
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