A lipoma is a common soft tissue growth, typically forming beneath the skin, but these benign, fatty tumors can also develop internally. When found in the large intestine, they are called colonic lipomas. They are the second most frequent type of non-cancerous tumor in the colon, after adenomatous polyps. Though rare (appearing in 0.2% to 4.4% of patients), they are the most common non-epithelial tumor in this part of the gastrointestinal tract. Colonic lipomas are often discovered incidentally during routine medical procedures or when they begin causing symptoms.
Defining Colonic Lipomas
A colonic lipoma is a non-cancerous growth composed entirely of mature fat cells (adipocytes) enclosed within a thin fibrous capsule. These growths are classified as mesenchymal tumors, meaning they arise from connective tissues rather than the organ’s lining. About 90% of colonic lipomas are located in the submucosa, the tissue layer beneath the inner lining of the colon wall. The remaining lipomas are found intramurally (within the muscle layer) or subserosally (on the outside surface of the colon).
They are typically solitary masses, though multiple lipomas occur in up to 20% of cases. Colonic lipomas vary significantly in size, ranging from a few millimeters up to 30 centimeters, but most are smaller than two centimeters. Unlike adenomatous polyps, these lesions are benign and do not carry a risk of becoming cancerous. Most colonic lipomas are found in the right side of the colon, particularly the cecum and ascending colon.
Clinical Presentation
The most frequent presentation is having no symptoms, with small masses often discovered incidentally during a colonoscopy or imaging study. If a lipoma grows beyond two centimeters, it is more likely to cause symptoms, which occur in 6% to 25% of cases. Symptoms generally relate to the physical space the growing mass occupies within the colon.
Symptoms often include intermittent abdominal pain, discomfort, or a change in bowel habits like diarrhea or constipation. When the lipoma exceeds four centimeters, it can lead to serious complications. One complication is gastrointestinal bleeding, which occurs when the overlying colon lining becomes irritated or ulcerated by the mass’s pressure. This bleeding can be chronic, leading to anemia, or occasionally severe.
The most severe complication is intussusception, where the lipoma acts as a lead point, causing one segment of the intestine to telescope into the next. This condition causes sudden, severe crampy abdominal pain, vomiting, and intestinal obstruction. Lipomas attached to the colon wall by a stalk (pedunculated) are particularly prone to causing intussusception. Since the symptoms of a large colonic lipoma can mirror those of colon cancer, accurate diagnosis is important.
Confirming the Diagnosis
The diagnostic process typically begins with a colonoscopy. A lipoma has a characteristic appearance: a smooth, yellowish, well-defined, soft mass protruding into the colon’s lumen. Specific endoscopic signs help differentiate a lipoma from other polyps, such as the “cushion sign” or “pillow sign,” where the mass indents when gently pressed with closed biopsy forceps.
Imaging studies are helpful in confirming the diagnosis by revealing the fatty nature of the growth. A computed tomography (CT) scan is reliable because it shows the mass as a well-circumscribed area with a characteristic low density consistent with fat. Magnetic resonance imaging (MRI) can also confirm the diagnosis by displaying signal intensity specific to adipose tissue.
While biopsy is standard for most colon polyps, it is often avoided or inconclusive for a submucosal lipoma. Since the lipoma is situated beneath the mucosal layer, a standard biopsy may only capture the normal overlying tissue. Repeated biopsies can sometimes lead to the “naked fat sign,” where yellow fat extrudes from the site, but this procedure risks bleeding or perforation. Endoscopic ultrasound (EUS) is often preferred, as it provides a detailed cross-sectional image showing the lipoma as a hyperechoic (bright) lesion originating from the submucosal layer.
Management and Treatment Options
Management is determined primarily by the lipoma’s size and whether it is causing symptoms. For small lipomas (generally less than two centimeters) that are asymptomatic, the standard procedure is “watchful waiting.” Since these masses pose minimal risk, they do not require immediate removal. Instead, the lipoma is monitored over time, typically with repeat colonoscopies, to ensure it does not grow or change.
Removal is necessary when a lipoma is symptomatic, causing abdominal pain, significant bleeding, or obstruction. Treatment options range from minimally invasive endoscopic removal to surgical resection. Smaller and pedunculated lipomas can often be safely removed endoscopically using a snare technique, similar to a standard polypectomy.
Endoscopic removal of large, sessile lipomas (greater than two centimeters) carries an elevated risk of complications, including perforation or severe bleeding, due to the electrical current needed to cut through the fatty tissue. In these cases, or when the lipoma has caused intussusception or bowel obstruction, surgical resection is preferred. Surgical options include minimally invasive laparoscopic procedures or traditional open surgery for very large or complicated masses.