Lipomas

Lipomas are the most common soft-tissue tumor. These slow-growing, benign fatty tumors form soft, lobulated masses enclosed by a thin, fibrous capsule. Although it has been hypothesized that lipomas may rarely undergo sarcomatous change, this event has never been convincingly documented. It is more probable that lipomas are at the benign end of the spectrum of tumors, which, at the malignant end, include liposarcomas . Because more than half of lipomas encountered by clinicians are subcutaneous in location, most of this article will be devoted to that subgroup. Additional information about other locations (eg, intramuscular, retroperitoneal, gastrointestinal) will be included as appropriate

Etiology

Speculation exists regarding a potential link between trauma and subsequent lipoma formation. One theory suggests that trauma-related fat herniation through tissue planes creates so-called pseudolipomas. It has also been suggested that trauma-induced cytokine release triggers pre-adipocyte differentiation and maturation. To date, no definitive link between trauma and lipoma formation has been prospectively demonstrated.

While the exact etiology of lipomas remains uncertain, an association with gene rearrangements of chromosome 12 has been established in cases of solitary lipomas, as has an abnormality in the HMGA2-LPP fusion gene.

Pathophysiology

Lipomas are common benign mesenchymal tumors. They may develop in virtually all organs throughout the body.

In the gastrointestinal tract, lipomas present as submucosal fatty tumors. The most common locations include the esophagus, stomach, and small intestine. Symptoms occur from luminal obstruction or bleeding.

Duodenal lipomas are mostly small but may become pedunculated with obstruction of the lumen. They may cause pain, obstructive jaundice, orintussusception in younger patients.^[5] Mucosal erosion over the lipoma may lead to severe bleeding, as demonstrated in the image below. Small intestinal lipomas occur mainly in elderly patients. They tend to be pedunculated submucosal lesions. They are more common in the ileum than in the duodenum or jejunum. As with duodenal lipomas, severe hemorrhage or intussusception may occur. Colonic lipomas are usually discovered on endoscopy. Gentle palpation with a biopsy forceps reveals the soft nature of the submucosal mass. A biopsy specimen of the mucosa may reveal underlying fat, the so-called naked fat sign. As with lipomas in other locations, colonic lipomas may cause pain with obstruction orintussusception.

Presentation

Symptoms in other sites depend on the location and can include the following:

• Lipomas in the major airways can cause respiratory distress related to bronchial obstruction. Patients may present with either endobronchial or parenchymal lesions.
• Previously undiagnosed lipomas of the oropharynx may also lead to airway difficulty at the time of intubation.
• Patients with esophageal lipomas can present with obstruction, dysphagia, regurgitation, vomiting, and reflux; esophageal lipomas can be associated with aspiration and consecutive respiratory infections.
• Cardiac lipomas are located mainly subendocardially, are rarely found intramurally, and are normally unencapsulated. They appear as a yellow mass projecting into the cardiac chamber.
• Intramediastinal lipomas may impinge on the superior vena cava, thereby leading to superior vena cava syndrome.
• Intestinal lipomas may manifest as classic obstruction, intussusception, volvulization, or hemorrhage.
• Lipomas arising from fat in the intramuscular septa cause a diffuse, palpable swelling, which is more prominent when the related muscle is contracted.
• Lipomas in intra-articular joint spaces or intraosseous sites, such as the calcaneus, may lead to joint dysfunction and pain that preclude normal ambulation.
• Lipomas may also arise in the dural or medullary components of the spinal cord, thereby leading to cord compression and attendant sequelae.^[7]
• Lipomas occur frequently in the breast but not as frequently as expected considering the extent of fat that is present.
• Lipomas may arise from the subcutaneous tissues of the vulva. They usually become pedunculated and dependent.