Lipomas

Lipomas are the most common soft tissue tumor. They are slow growing benign tumors of fatty tissue that form a lobulated soft mass enclosed by a thin fibrous capsule. Lipomas may rarely undergo sarcomatous change; however, the event has never been convincingly documented.

Problem: Lipomas may easily be confused with other tumors for the following reasons:

Because liposarcomas occur most commonly in the retroperitoneum and on the legs, a tissue diagnosis is indicated in tumors at these locations to exclude the possibility of a malignancy.

A lipoma located in the breast is mammographically radiolucent and can be confused with a pseudolipoma, the soft tissue mass that may surround a small scirrhous cancer.

Conversely, lipomatous lesions in the adrenal gland that have calcifications on radiological examinations have been confused with teratoma.

A lipoma of the liver has been confused with a metastasis in a patient with anamnestic adenocarcinoma of the colon.

A palpable inguinal mass without an identifiable hernia defect at time of laparoscopy may indicate the presence of a lipoma of the spermatic cord.

Frequency: Lipomas occur in 1% of the population. In the intestine, lipomas constitute 16% of benign small neoplasms, which is less than leiomyomas (18%) and more than adenomas (14%).

Pathophysiology: Lipomas may develop in virtually all organs throughout the body. More than half of all gastrointestinal lipomas are in the esophagus, stomach, and small intestine. They are submucosal tumors of adipose tissue, they occur most commonly in the ileum, and they may be single or multiple. Duodenal lipomas are mostly small but may become pedunculated with obstruction of the lumen. They may cause pain, obstructive jaundice, or intussusception in younger patients. Mucosal erosions over the lipoma may lead to severe bleeding. Lipomas in the small intestine occur mainly in elderly patients. They tend to be pedunculated, with some being submucosal, and they are more often found 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. They may cause pain with obstruction or intussusception.

Lipomas may develop at other rare locations, as reported by numerous case reports. Lipomas have been described in the adrenal gland, the parotid gland, the parapharyngeal space, the mediastinum, the pleura, the major airways, the heart (causing ventricular tachycardia), in the superior vena cava, the spermatic cord, the brain, and at intraspinal locations. Childhood lipomas have been reported at rare locations such as the mesenterium or the esophagus, causing respiratory distress.

Lipoma variants include lipoblastomas and hibernomas. Lipoblastomas occur almost exclusively in infants and children. They have a benign clinical course with a low recurrence rate after surgical excision. Hibernomas, also rare, derive their name from the morphologic resemblance to the brown fat of hibernating animals. They presumably arise from fat that may occur in the back, hips, or neck in adults and infants.

Clinical: Lipomas are most often asymptomatic. When they arise from fatty tissue between the skin and deep fascia, typical features include soft fluctuant feel, lobulation, and the free mobility of overlying skin. Symptoms depend on location and can include the following:

• Patients with esophageal lipomas can present with obstruction, dysphagia, regurgitation, vomiting, and reflux; esophageal lipomas can be associated with aspiration and consecutive respiratory infections.

• Lipomas in the major airways can cause respiratory distress related to bronchial obstruction. Patients may present with either endobronchial or parenchymal lesions.

• Lipomas arising from fat in the intramuscular septa cause a diffuse palpable swelling, which is more prominent when the related muscle is contracted.

• Lipomas occur frequently in the breast but not as frequently as expected considering the extent of fat that is present.

• Lipomas in the intestines (ie, duodenum, jejunum, colon) may cause abdominal pain from obstruction or intussusception, or they may become evident through hemorrhage.

• Cardiac lipomas are located mainly subendocardially, rarely intramurally, and are normally unencapsulated. They appear as a yellow mass projecting into the cardiac chamber.

• Lipomas may arise from the subcutaneus tissues of the vulva. They usually become pedunculated and dependent.

• Lipomas are removed for the following reasons:
  • Cosmetic reasons

  • To evaluate their histology, particularly when liposarcomas must be ruled out (important in mediastinal tumors)

  • When they cause symptoms

  • When they grow and become larger than 5 cm

• Obtain biopsies of large lipomas or those tethered to fascia to rule out a liposarcoma.