A submucosal lipoma is a non-cancerous growth composed of mature fat cells, known as adipocytes. The term “submucosal” indicates its location in the layer of tissue just beneath a mucous membrane. These tumors are almost always benign and characterized by their slow growth. While they can form in any organ, they are most commonly found within the gastrointestinal (GI) tract and are often discovered incidentally during medical procedures.
Common Locations and Symptoms
The vast majority of submucosal lipomas occur within the gastrointestinal tract, though their frequency varies by location. The colon, or large intestine, is the most common site, with studies indicating that up to 70% of GI lipomas are found there. Following the colon, the small intestine is the next most frequent location, with the stomach and esophagus being comparatively rare sites.
Many submucosal lipomas are completely asymptomatic. When symptoms do arise, they are directly related to the size and specific location of the tumor, as lipomas smaller than 2 centimeters are less likely to cause noticeable issues.
In the colon and small intestine, a larger lipoma can lead to symptoms like colicky abdominal pain, alterations in bowel habits such as constipation or diarrhea, and bleeding. Bleeding occurs if the mucosal tissue stretched over the lipoma becomes ulcerated, leading to blood in the stool. In less common scenarios, a large lipoma can act as a lead point for an intussusception, a serious condition where one segment of the intestine telescopes into another, causing an obstruction.
Elsewhere in the GI tract, a submucosal lipoma in the stomach may cause feelings of premature fullness, indigestion, or gastric outlet obstruction. In the esophagus, even a moderately sized lipoma can interfere with the passage of food, leading to difficulty swallowing (dysphagia).
The Diagnostic Process
The initial discovery of a submucosal lipoma often happens during an endoscopic procedure, such as a colonoscopy or an upper GI endoscopy. During the examination, a gastroenterologist will observe a smooth, often yellowish bulge. A characteristic feature that raises suspicion for a lipoma is the “cushion sign,” where the mass can be gently indented with a biopsy forceps, only to regain its shape once pressure is released.
While endoscopy provides the first visual clue, advanced imaging is used to confirm the diagnosis. Endoscopic ultrasound (EUS) uses sound waves from a small probe on an endoscope to create detailed images of the gastrointestinal wall layers. This allows a physician to see that the mass originates from the submucosal layer and has a uniform, bright appearance characteristic of fatty tissue.
Other imaging modalities like computed tomography (CT) scans and magnetic resonance imaging (MRI) are also highly effective. A CT scan can clearly identify the lipoma by showing a well-defined mass with a specific low-density measurement (between -40 and -120 Hounsfield units) that is diagnostic for fat. This imaging helps determine the precise size and extent of the lipoma for treatment planning.
A standard biopsy taken from the surface of the mass during endoscopy can be inconclusive. Because the lipoma is located under the normal mucous membrane, a superficial biopsy may only collect healthy mucosal cells, failing to reach the fatty tumor. In some cases, repeated biopsies at the same site may expose the underlying fat, a finding referred to as the “naked fat sign.”
Treatment and Removal Options
The management strategy for a submucosal lipoma is determined by its size and whether it is causing symptoms. For small, asymptomatic lipomas, typically those less than 2 centimeters, the standard approach is observation or “watchful waiting.” This involves periodic monitoring with follow-up endoscopies to ensure the lipoma is not growing significantly or causing problems.
Removal of a submucosal lipoma is recommended when it becomes symptomatic, causing issues like bleeding, pain, or obstruction. Intervention is also advised for lipomas that are large (often greater than 2 cm) or if there is any uncertainty in the diagnosis. The decision to remove the growth is made to alleviate current symptoms and prevent potential future complications.
For many lipomas, endoscopic removal is the preferred method as it is the least invasive option. Techniques such as endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) allow for the tumor to be removed through an endoscope without external surgical incisions. These procedures involve injecting a solution under the lipoma to lift it away from the deeper muscle layer before it is snared and cut away.
Surgical resection is generally reserved for specific situations, such as for very large lipomas or those in areas difficult to access with an endoscope. It is also used when an endoscopic removal attempt is unsuccessful or deemed unsafe. Depending on the tumor’s size and location, surgery may be performed laparoscopically or through a traditional open procedure, which involves removing the segment of the organ containing the lipoma. The prognosis following removal is excellent since the condition is benign, and recurrence at the same site is rare.