Description

• Lipomas are the most common benign SC tumors.
• They are composed of mature fat cells, enveloped by a thin, fibrous capsule.
• Slow growing, often asymptomatic, and usually have a soft doughy feel on palpation
• Some lipomas are believed to have developed following blunt trauma.
• Lipomas rarely, if ever, become malignant, but must be differentiated from liposarcomas and other tumors.

Epidemiology

• They can occur at any age, but are most common in middle-aged adults, peaking in the 40–60-year age group.
• They are rare in children.

Incidence
The incidence of lipomas is 1/1,000 individuals annually.

Prevalence
Occur in ~1% of population

Risk Factors

• Soft-tissue trauma frequently has been cited as a cause, especially if the patient develops a posttraumatic hematoma.
• Alcohol consumption may be a predisposing factor for Madelung disease, or benign symmetric lipomatosis, with lipomas on the head, neck, shoulders, and proximal upper extremities. This may present with the characteristic “horse collar” cervical appearance, resulting in swallowing or respiratory problems and sudden death.

• May appear as a hereditary syndrome in patients with hereditary multiple lipomatosis, an autosomal dominant condition. This is found most frequently in men, characterized by extensive, symmetric, sometimes giant lipomas, mostly on extremities and trunk.
• Congenital lipomas have been observed in children.

Pathophysiology

• The pathogenetic link between soft-tissue trauma and the formation of posttraumatic lipomas is still controversial.
• There are 2 potential explanations to correlate soft-tissue trauma and adipose tissue tumor growth:
  • The 1st is the formation of so-called posttraumatic pseudolipomas by prolapsing adipose tissue through fascia resulting from direct impact.
  • A 2nd possibility points toward lipoma formation as a result of preadipocyte differentiation and proliferation mediated by cytokine release following soft-tissue trauma and hematoma formation.

Etiology

They are reported to occur after trauma, but most are idiopathic.

Commonly Associated Conditions

• Admixture of other tissue types leads to fibrolipomas, angiolipomas, and myolipomas.
• Unusual presentations of lipoma can occur, like giant lipomas in hereditary multiple lipomatosis, adiposis dolorosa (multiple tender, diffuse lesions), Gardner syndrome with intestinal polyposis, and Madelung disease (numerous symmetrically distributed lipomas of the upper trunk).
• Liposarcomas rarely develop from benign lipomas. They can occur anywhere in the body, mostly in deep structures.