What is a Lipoma?
A lipoma is a slowly growing lump of fatty tissue. It is soft to the touch, painless and moves readily with pressure. They are usually present under the skin, but occasionally they can be located in deeper areas of the skin. In most cases lipomas reach up to 1 inch (or around2 to 3 cm, but in rare cases people have giant lipomas that can grow more than 10 cm.
Lipomas are usually harmless and they are not cancerous. Removal of the lipoma is not necessary but can be done if it causes discomfort or pain.
Lipomas are the most common type of noncancerous soft-tissue tumor, affecting 2% of the population. It typically occurs in adults (males more than females) between 40 to 60 years old.
- Generally small: 2-3 cm.
- Soft and doughy.
- Situated under the skin.
- Sometimes painful: depending on its location.
- Encapsulated: do not spread to surrounding tissue.
- Moveable: they move when you touch them.
- Round or oval shaped.
The causes of lipomas are not completely known. They may appear due to a hereditary component with studies showing the HMG I-C gene has a correlation with lipoma development. Other studies show that minor injuries can trigger the growth of a lipoma, this is called post-traumatic lipoma.
Lipoma: Risk factors
Lipomas are more common in people between the ages of 40 to 60. They are rarely seen in children. Obesity and family history can increase the chances of getting lipomas. Other conditions associated with lipomas are:
- Gardner Syndrome: autosomal dominant form of polyposis.
- Dercum disease: rare condition characterized by obesity and fatty tumors.
- Lipomatosis: autosomal dominant condition characterized for multiple lipomas present on the body.
Types of Lipoma
- Adenolipomas: they contain entrapped eccrine glands. They are superficially located and might not be well encapsulated. This term is also used for a variety of lesions containing fat, but in these cases they are not considered a lipoma.
- Angiolipomas: these are painful subcutaneous nodules. They are composed of mature fat with numerous small blood vessels.
- Hibernomas: these are lipomas of brown fat.
- Intradermal spindle cell lipomas: these are most common in women and are distributed with relatively the same frequency throughout the body.
- Fibrolipoma: it is a lipoma with focal areas of large amounts of fibrous tissue, if they are located alongside the nerve trunk they can lead to nerve compression, this are called neural fibrolipomas. They must not contain atypical cells.
- Pleomorphic lipomas: these are characterized by floret giant cells with overlapping nuclei. They usually appear in the back and neck of elderly men.
- Spindle cell lipomas: they are asymptomatic, slow growing and subcutaneous. They appear in older men especially in the back, neck and shoulders.
- Superficial subcutaneous lipomas: they are the most common type of lipoma. They lie below the surface of the skin and usually located in the trunk, thighs and forearms. They can also be found anywhere in the body where fat is located.
Lipomas usually don’t cause pain. But they can be uncomfortable if they develop near a joint or if they are pressing a nerve. In most cases people with lipoma don’t experience any symptoms.
You should go see a doctor if a lipoma is:
- Growing in size,
- Being painful,
- Becoming red or hot,
- Turning into an immovable lump,
- Causing visible changes in the overlying skin.
Lipomas turning into malignant liposarcomas is very rare. Deep lipomas have a greater tendency to recur than superficial lipomas, even though most liposarcomas are not produced from pre-existing benign lesions.
There are usually 4 cases in which lipomas might cause the compression of a nerve causing pain.
- Solitary lipomas can eventually compress a nerve.
- Encapsulated lipomas can be sometimes localized near a nerve, like an intrinsic lesion.
- Lipofibromatous hamartoma, which is an extremely rare benign intranervous tumor.
- Macrodystrophia lipomatosa is a congenital disorder characterized by a localized overgrowth of a part of an extremity.
Lipomas can usually be diagnosed with a simple physical exam. If the lipoma causes pain or if it is too large, an analysis might be required to check if it is cancerous. This can be done with a biopsy, ultrasound scans, MRI scan or CT scan.
Biopsy: it is necessary in some cases to confirm the diagnosis. A sample of the tissue is removed and then studied and examined under a microscope.
Ultrasound: lipomas appear as soft variably echogenic masses, commonly encountered on ultrasound. But if it is encapsulated it may be difficult to spot.
Magnetic Resonance Imaging (MRI): it uses a magnetic field and computer generated radio waves to create detailed images of organs and tissue. This is the modality of choice for imaging lipomas. It is not only used to confirm a diagnosis (like a suggestive diagnosis made by ultrasound or ct), but also to assess atypical features suggesting liposarcoma. Lastly, an MRI is able to better demonstrate the surrounding anatomy.
Computerized Tomography (CT): this scan combines a series of X-ray images from different angles around your body. Deeper or larger lesions might have scattered areas of internal soft tissue density, often more apparent on CT vs MRI. They may represent areas of fat necrosis, fibrous tissue, blood vessels or muscle fibres. This lesion can not be differentiated from liposarcomas by imaging.
Treatment of lipomas is not usually needed, unless they become painful or restrict movement. Another reason for removal of lipomas is due to cosmetic reasons. They are also removed and studied to check if they are not a dangerous type of tumor, such as liposarcoma, as this is not known until removed and medically examined. Only 1-2% of lipomas recur after excision.
Another possible treatment is liposuction as lipomas are soft and have a small component of connective tissue. Liposuction results in less scarring, but in large lipomas it might fail to completely remove the tumor.
New treatments are being developed in order to reduce scarring, such as injecting compounds that trigger lipolysis (steroids, phosphatidylcholine for example). There are others based on tissue-targeting heating, including cauterization, electrosurgery and harmonic scalpel.