Lipomas are common benign skin growths that can be seen as solitary lesions and frequently as multiple dermal nodules scattered about the skin. The lipoma is an overgrowth of the fibrofatty adipose tissue in the subcutaneous tissue plane. Patients with multiple lipomas often describe a familial inheritance pattern.
Clinical Findings: Lipomas are often small (1-2 cm), soft, subcutaneous nodules that are slow growing and freely moveable underneath the skin. Some lipomas become quite large (>5 cm in diameter), and they can be a cause for concern due to interference with movement and the possibility of malignant degeneration into a liposarcoma. There are no overlying epidermal changes, and there is no connection to the epidermis. Most often they are asymptomatic, but they can become painful if traumatized.
In stark contrast, a rare variant called the angiolipoma is almost always tender and multiple in nature. Angiolipomas contain a much higher percentage of blood vessels throughout the lobule of adipose tissue, and the diagnosis is made based on this histopathological finding. These tumors are benign and have no familial inheritance pattern.
The differential diagnosis of a lipoma is broad and can include other dermal tumors; however, the clinical examination findings are often diagnostic. Occasionally, a small lipoma can be confused with an epidermal inclusion cyst, pilar cyst, lymph node, or adnexal tumor. Large, freely movable, rubbery nodules that are slow growing are easily diagnosed clinically as lipomas.
Lipomas occur most commonly on the trunk and extremities. They most often affect women in their third through fifth decades of life but can affect people of any age and sex. There is no race predilection. They rarely affect the face, except for the subfrontalis lipoma, which occurs underneath the frontalis muscle on the forehead.
Rare syndromes of adipose tissue have been described, including benign symmetric lipomatosis, adiposis dolorosa (Dercum’s disease), and familial multiple lipomatosis. The best described of these syndromes is benign symmetric lipomatosis, also known as Madelung’s disease. In this condition, there is massive proliferation of adipose tissue on the neck and upper arms of men. The patients take on the appearance of a body builder.
Pathogenesis: The exact cause is unknown. Lipomas are believed to be an overgrowth of normal tissue in a normal location. The tumor lobules are indistinguishable from normal adipose tissue. A genetic pattern of inheritance has been described, but no specific gene defect has been located.
Histology: Lipomas are composed of mature adipose tissue. The lobules are separated by fibrous septa that contain the blood supply for the adipose cells. Lipomas have a fibrous capsule enclosing the adipose lobules. Angiolipomas are described as those fatty tumors in which 10% to 50% of the mass is composed of blood vessels. The various rare lipomatosis variants are identical in appearance histologically to a common lipoma.
Treatment: No therapy is required for these benign skin tumors. Solitary lipomas can be treated with a simple excision or with liposuction. Subfrontalis lipomas are more difficult to remove, because the surgeon must dissect below the frontalis muscle to locate the lipoma. Small lipomas have been treated with intralesional steroid injection to take advantage of the steroid’s atrophogenic effects. Injections with deoxycholate have also been effective. Large, fast-growing lipomas should be removed to rule out malignant transformation into a liposarcoma. Compared with lipomas, liposarcomas are typically faster growing, firmer, and tender in nature.