Nonepithelial Colorectal Tumors

Benign Lymphoid Hyperplasia

A benign lymphoid polyp is an aggregation of lymphoid tissue with a covering of normal mucosa. These lesions are most common in the rectum and the distal sigmoid, where they can be single or multiple, broad based, or have a short pedicle. They are homogeneous in appearance and are usually pale. These lesions are usually small—2 to 4 mm in diameter—but sometimes mucosa-associated lymphoid tissue can measure several centimeters. Lymphoid hyperplasia is more prominent in children and young adults, in whom the polyps are numerous and can mimic polyposis. In daily practice, lymphoid polyps are removed during colonoscopy because they are difficult to differentiate from small adenomas or serrated polyps. This is especially the case when polyp detection rate is an important quality indicator for colonoscopy. Usually, the pathologist makes the diagnosis. Benign lymphoid polyps need no follow-up and carry no risk.

Lipomas

Although lipomas are the second most common neoplasm of the colon after adenomas, they are uncommon, with an incidence of less than 1%. Gender distribution is equal, and the average age at diagnosis is 62.4 years. Lipomas are submucosal lesions ranging in size from 0.5 mm to larger than 6.5 cm. They can be pedunculated or sessile and are most often found in the right colon, followed by the transverse colon, sigmoid colon, and rectum. Although most lipomas are asymptomatic and are found incidentally, they can cause intermittent bowel obstruction (if the lipoma is near the ileocecal valve), colocolonic intussusception, or prolapse through the rectum.

The typical endoscopic appearance of a submucosal lipoma is a yellowish, smooth polyp with a broad base or a short, thick stalk. The mucosal pit pattern is endoscopically normal, although the submucosal position of the lipoma causes stretching of the mucosa, allowing the endoscopist to see the normal blood vessels. The “pillow sign” is the classic endoscopic diagnostic maneuver. Biopsy forceps push on the center of the presumed lipoma, which indents and then gradually regains its shape, much like a pillow does when it is poked. A superficial biopsy of a lipoma yields only normal mucosa. However, when a diathermy snare is used to remove overlying mucosa, fat protrudes from this site. An important differential, especially in right-sided lipomas, is a carcinoid tumor. This tumor also looks yellow, but in contrast to lipomas, it is hard and fixed, with no “pillow sign.”