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General Surgery > Abdomen
Lipomas
Article Last Updated: Apr 17, 2006
AUTHOR AND EDITOR INFORMATION
Section 1 of 12  
Author: Carol E H Scott-Conner, MD, PhD, Professor, Department of Surgery, University of Iowa College of Medicine
Carol E H Scott-Conner is a member of the following medical societies: American Association for Cancer Research, American Association for the Surgery of Trauma, American Burn Association, American Cancer Society, American College of Gastroenterology, American College of Surgeons, American Medical Association, American Society for Gastrointestinal Endoscopy, Association for Academic Surgery, Association for Surgical Education, Association of VA Surgeons, Iowa Medical Society, Sigma Xi, Society for Surgery of the Alimentary Tract, Society of American Gastrointestinal and Endoscopic Surgeons, Society of Critical Care Medicine, Society of Surgical Oncology, Society of University Surgeons, and Southeastern Surgical Congress
Coauthor(s):
Klaus Radebold, MD, PhD, Research Associate, Department of Surgery, Yale University School of Medicine
Editors: Juan B Ochoa, MD, Assistant Professor, Department of Surgery, University of Pittsburgh; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; David L Morris, MD, PhD, Professor, Department of Surgery, St George Hospital, University of New South Wales, Australia; Paolo Zamboni, MD, Professor of Surgery, Chief of Day Surgery Unit, Chair of Vascular Diseases Center, University of Ferrara, Italy; John Geibel, MD, DSc, MA, Professor, Department of Surgery, Section of Gastrointestinal Medicine and Department of Cellular and Molecular Physiology, Yale University School of Medicine; Director of Surgical Research, Department of Surgery, Yale-New Haven Hospital
Author and Editor Disclosure
Synonyms and related keywords:
liposarcomas, pseudolipoma, teratoma, adenolipomas, angiolipomas, hamartoma, cardiac lipomas, soft tissue tumor, benign tumors of fatty tissue, benign small neoplasms, submucosal tumors of adipose tissue, duodenal lipomas, colonic lipomas, lipoblastomas, lipoma, hibernomas, esophageal lipomas, intussusception, intestinal lipomas, intestinal obstruction, intramuscular lipoma, pediatric lipoblastomas, benign mesenchymal tumors, lipomas of the lung, breast lipomas, subcutaneous lipomas, lipomas of the vulva, frontalis-associated subfascial lipoma
Lipomas are the most common soft tissue tumor. These slow-growing, benign fatty tumors form lobulated soft 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 (see Pathophysiology). 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.
Problem
Lipomas must be differentiated from other masses or tumors.
In the subcutaneous location, the primary differential diagnosis is a sebaceous cyst or an abscess. Sebaceous cysts are also rounded and subcutaneous. They can be differentiated from lipomas by their characteristic central punctum and the surrounding induration. Treatment requires removal of a small ellipse of overlying skin to avoid entering the cyst. Abscesses typically have overlying induration and erythema. Incision and drainage is the appropriate management.
Hibernomas are uncommon tumors that arise from brown fat. They are also benign but with a slightly greater tendency to bleed during excision and to recur if intralesional excision is performed.
Atypical lipomatous tumors are considered to be well-differentiated liposarcomas. They have a predilection for local recurrence but do not generally metastasize. This diagnosis should be suspected when a fatty tumor is encountered in an intramuscular or retroperitoneal location.
Liposarcomas are malignant tumors that arise from adipocytes. They may recur locally and may metastasize. Fatty tumors of the retroperitoneum or in intramuscular locations should be considered to be potential liposarcomas until proven otherwise.
In the breast, a lipoma will be mammographically radiolucent. It must be differentiated from a similar benign tumor, a mammary hamartoma, and the pseudolipoma (a 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. Many of these are angiomyolipomas.
In the spermatic cord, a finger of retroperitoneal fat termed a "lipoma of the cord" is frequently encountered during hernia repair. Removal is advocated to allow the internal inguinal ring to be tightened around the cord and to minimize the risk of recurrence of the hernia. During laparoscopic exploration for a palpable inguinal mass, no identifiable peritoneal orifice may be found if the inguinal mass purely consists of a lipoma of the cord.
Frequency
Lipomas occur in 1% of the population. Most of these are small subcutaneous tumors that are removed for cosmetic reasons. These subcutaneous lipomas will be considered separately from lipomas in other locations in the discussion below. In the intestine, lipomas constitute 16% of benign small neoplasms, which is less than leiomyomas (18%) and more than adenomas (14%).
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, or intussusception in younger patients. Mucosal erosion over the lipoma may lead to severe bleeding (see Media file 1). 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 other locations, they may cause pain with obstruction or intussusception. As noted above, a fatty protrusion of preperitoneal fat termed a "lipoma of the spermatic cord" is a common finding on groin exploration for hernia repair. Numerous case reports document observation of lipomas in other rare locations. Lipomas have been described in the adrenal gland, the parotid gland, the parapharyngeal space, parotid gland, mediastinum, pleura, the major airways, the heart (causing ventricular tachycardia), in the superior vena cava, the brain, and at intraspinal locations. Childhood lipomas have been reported at rare locations, such as the mesentery or the esophagus, causing respiratory distress. Mixed histologies, such as angiolipomas and fibrolipomas, are often encountered and are usually benign. Differentiation from liposarcoma may be difficult. Other fatty tumors include lipoblastomas, hibernomas, atypical lipomatous tumors, and liposarcomas. 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. Atypical lipomatous tumors are generally considered to be low-grade sarcomas, with a strong propensity to recurrence but little metastatic potential. Liposarcomas are true mesenchymal malignancies.
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. A characteristic "slippage sign" may be elicited by gently sliding the fingers off the edge of the tumor. The tumor will be felt to slip out from under, as opposed to a sebaceous cyst or an abscess that is tethered by surrounding induration. The overlying skin is typically normal.
Symptoms in other sites depend on the 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 subcutaneous 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
- 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.
- The anatomy depends on the tumor site.
- Subcutaneous lipomas are usually not fixed to the underlying fascia.
- The fibrous capsule must be removed to prevent recurrence.
No contraindications to removing a lipoma exist, unless the patient is unfit for surgery. Benign lipomas are simply "shelled out" with complete removal of the capsule in an extracapsular plane. This is an inadequate operation for a liposarcoma, and, hence, performing an initial biopsy to exclude this lesion may be considered for large fatty tumors or those in the retroperitoneum or intramuscular spaces.
Imaging Studies
- For most subcutaneous lipomas, no imaging studies are required.
- Lesions in the gastrointestinal tract may be seen on GI contrast studies (see Media file 2).
- Imaging studies for lipomas in atypical locations (or where the differential diagnosis includes sarcoma) include ultrasonography, computerized tomography scans, and magnetic resonance imaging.
- MRI has been recommended as a reliable preoperative investigation.
- It has been employed in intramuscular lipoma, pediatric lipoblastomas, and others. The findings of intramuscular lipomas, for example, vary from small homogeneous masses to large inhomogeneous lesions with infiltrative margins.
- However, similar to computed tomography scan, MRI does not allow an absolute reliable distinction between a lipoma and a liposarcoma.
- When computerized tomography scan is employed, Hounsfield units less than 50 are indicative for a soft tissue tumor composed of fat, although no discrimination can be made between a benign lipoma and a malignant liposarcoma.
- Because lipomas are radiolucent, soft tissue radiographs may sometimes be useful.
Diagnostic Procedures
- Biopsies are normally not indicated for small subcutaneous lesions because the entire tumor is usually removed.
- All imaging techniques have been combined with fine-needle aspiration, and this combination increases the accuracy of diagnosis.
- Obtaining tissue samples from different tumor components is important.
Histologic Findings
- Lipomas are benign mesenchymal tumors derived from adipocytes. Several variants have been described, including the following:
- Adenolipomas, a variation of lipomas that may occur in the breast, often have a marked fibrotic component. They are best regarded as a hamartoma.
- Angiolipomas contain many small vessels.
- Cardiac lipomas may calcify following fat necrosis. Microscopically, they are comprised of fatty tissue with interlacing muscle fibers.
- Fine-needle aspiration biopsies of a lipoblastoma contain multivacuolated lipoblasts, myxoid areas, and a plexiform capillary network.
Medical therapy
- Medical therapy includes endoscopic excision of tumors in the upper gastrointestinal tract (ie, esophagus, stomach, duodenum) or the colon.
- Colonoscopic snare removal has been described but may be associated with perforation if the base is broad.
- Japanese authors reported a safe technique using a bipolar snare and clipping the mucosa of the defective region. Otherwise, surgical removal is indicated.
Surgical therapy
Complete surgical excision with the capsule is essential to prevent local recurrence. These lesions may be lobulated, and it is essential that all lobules be removed. The therapy depends on the location of the tumor.
Subcutaneous lipomas are removed for cosmetic reasons, and, hence, a cosmetically-pleasing incision should be used. The incision is usually placed directly over the mass and oriented to lie in a line of skin tension. Liposuction is an alternative that allows removal through a very small incision that may be located remote from the actual tumor. Alternatively, the lesion may be approached with advanced minimal access tissue dissection methods using a dissecting balloon. The latter 2 methods allow the incision to be placed in an inconspicuous location. For example, axillary incisions may be used to remove lipomas from the back with these techniques.
For more unusual locations, the method of removal must be tailored to the site.
- Local removal is indicated in lipomas narrowing the major airways. Lipomas of the lung may require resection of pulmonary parenchyma or the involved airway.
- Local removal is indicated in intestinal lipomas causing obstruction.
- If esophageal lipomas cannot be endoscopically removed, surgical excision is indicated.
- Breast lipomas are excised if their nature is in doubt. With modern breast imaging techniques, this is rarely necessary.
- Intestinal, particularly duodenal, lipomas should be removed either endoscopically or surgically because they can cause obstruction, jaundice, or hemorrhage. A solitary case of a liposarcoma in the ileum has been described.
- Lipomas of the vulva are locally excised.
Preoperative details
Because all lipomas are radiolucent, findings on soft tissue radiographs can be diagnostic but are only indicated when the diagnosis is in doubt.
Intraoperative details
- Tumors can usually be enucleated. They may recur if not properly removed, and this includes removal of the capsule.
- Hibernomas tend to be highly vascular.
- Lipomas in other locations may present unique difficulties during removal; for example, a man presenting with a frontalis-associated subfascial lipoma as a protruding mass on the lateral forehead may be difficult to dissect because of the highly vascular muscle that invests it.
- Lipomas of the gastrointestinal tract can frequently be shelled out of their submucosal location. The duodenal lipoma shown in Media files 1-2 was excised with a disk of overlying ulcerated mucosa.
Follow-up
The patient should consult a physician if signs of recurrence appear.
Subcutaneous lipomas are primarily cosmetic issues. Lipomas in other locations may cause luminal obstruction or hemorrhage. Media files 1-2 illustrate a duodenal lipoma that caused gastrointestinal hemorrhage and required removal.
Outcome and prognosis are excellent for benign lipomas. Recurrence is uncommon, but they may occur if excision is incomplete.
Liposuction may be employed more often in small facial lipomas because favorable aesthetic results have been obtained through strategically placed incisions. Liposuction is indicated for the treatment of medium (ie, 4-10 cm) and large (ie, >10 cm) lipomas; in small lipomas, no advantage has been reported because these tumors can be extracted through small incisions.
Lipomas have been reported to form as an unusual complication of liposuction and to follow trauma. The mechanism is unknown. Research on genetic markers of atypical lipomatous tumors and liposarcomas is ongoing. These tumors have been shown to express receptors for leptin.
| Media file 1:
Upper gastrointestinal series shows duodenal lipoma with central ulceration where the overlying mucosa has thinned, ulcerated, and bled. |
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Media type: X-RAY
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| Media file 2:
Duodenal lipoma resected through a duodenotomy. Overlying mucosa with central ulceration removed and lobulated fatty tumor shelled out intact with capsule. The mucosa was then sutured closed, and the duodenotomy closed. The stitch was placed to orient the specimen for pathologic examination. |
 | View Full Size Image | |
Media type: Photo
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Lipomas excerpt Article Last Updated: Apr 17, 2006
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