Intestinal Polyps

Polyps are nodules of tissue that project above the mucosa; they can occur throughout the GI tract, but are most common in the colon. Polyps are usually asymptomatic, but can cause bleeding or other GI issues, depending on their size. Pedunculated: Pedunculated polyps hang from a stalk. Ex: Pedunculated adenomas have a stalk that comprises an outgrowth of submucosa covered in muscularis mucosae and adenomatous epithelium – show that the epithelium is thicker, i.e., overgrown, at the top of the polyp. See Gross Structure See Histology of Pedunculated Polyp Sessile: Sessile polyps are characterized by overgrown epithelia that raises above the normal tissue but in a flat, shelf-like way (sessile means fixed at the base without a stalk). See Histology of Sessile Polyp NEOPLASTIC POLYPS Adenomatous polyps Aka, adenomas Very common. Most colorectal cancers arise from adenomas. Adenomas can range in size from small to large; larger polyps are more often malignant. The histology is glandular, and can be categorized as villous, tubulovillous, or tubular.

• Villous adenomas are characterized by long, finger-like projections; some authors report that villous adenomas are more likely to be malignant.

See histology of villous tumor

• Tubular adenomas are characterized by disorganized and irregular tubular glands.

Tubulovillous adenomas comprise a combination of villous and tubular structures. See histology of tubular adenoma Common features of the histological subtypes are elongated, crowded nuclei and loss of goblet cells. Neoplastic subtypes of serrated polyps Sessile serrated lesions are flat, variable in size, and have a mucinous cap; these are often found in the proximal colon. Sessile serrated lesions have irregular crypts that are dilated and branching with a "T" or "boot-shaped" bottom. Traditional serrated adenomas are larger and have villous architectures; these are more often found in the distal colon. Be aware that the nomenclature used for serrated polyps has undergone changes as our understanding of them has evolved. NON-NEOPLASTIC POLYPS Hyperplastic polyps are a third subtype of serrated polyps. As opposed to the dilated crypts of the neoplastic subtypes we just learned, hyperplastic polyp serration tends to be concentrated towards the upper region of the crypts. Hyperplastic polyps are the most common polyp, and that they are often found co-existing with adenomas. They are small (5 mm or less), with a flat or oval shape; they are often found in the distal colon. Two subtypes are goblet rich and micro-vesicular; the clinical significance of these subtypes is uncertain. The apical crypts of hyperplastic polyps have a serrated or sawtooth appearance, with goblet cells and mucin droplets. See histology of hyperplastic polyp.jpg) Unfortunately, it can be very difficult to tell hyperplastic polyps from sessile serrated polyps based on histology alone; researchers are working on molecular methods to distinguish the nonneoplastic from neoplastic polyps. Hamartomatous polyps comprise normal tissues with abnormal distributions. Though rare overall, they are the most common polyp found in children, and are typically solitary and benign. There are two histological subtypes:

• Peutz-Jeghers polyps are characterized by ribbons of arborizing smooth muscle (notice the tree-like appearance).
• Juvenile polyps comprise large dilated cystic glands. Be aware that "juvenile" refers to the histopathology, not the age of onset.

Mucosal polyps, which are clinically insignificant, and submucosal polyps, which are rare (these include lipomas, leiomyomas, fibromas, etc.). Inflammatory polyps and pseudopolyps are associated with inflammatory bowel disorders; they comprise inflammatory cells mixed with epithelial and stromal components. Inherited disorders characterized by multiple polyps and increased cancer risk. See Gross Sample Familial adenomatous polyposis (FAP) is the most common polyposis syndrome. Caused by mutations in the APC tumor suppressor gene. Penetrance varies, and patients develop 100s-1000s of adenomas ("attenuated familial adenomatous polyposis" is characterized by fewer than 100 polyps). If untreated, FAP is associated with a 100% chance of developing colorectal cancer by age 40. Extracolonic manifestations, including desmoid tumors and gastric polyps are common, and two variants of FAP are recognized by their propensity for specific manifestations: Gardner syndrome is FAP with osteomas, often of the mandible or skull, and skin/soft tissue tumors. Turcot syndrome is FAP with CNS tumors, often medulloblastomas. Hamartomatous polyposis syndromes Inherited autosomal disorders; two of the syndromes are named for their polyp subtypes. Peutz-Jeghers polyposis syndrome is characterized by pigmented macules on mucous membranes and skin (often in/around the mouth and nose). See pigmented macules Complications in children tend to directly result from mechanical issues related to the polyps, such as intussusception, torsion, and obstruction. In adults, complications include reproductive and GI cancers. Be aware that Peutz-Jeghers polyps are often found in the small intestine and stomach, whereas we've focused on colon polyps for most this tutorial. Juvenile polyposis syndrome is characterized by cutaneous and skeletal manifestations (for example, telangiectasia). Other hamartomatous polyposis syndromes include PTEN-Hamartoma syndromes and hereditary mixed polyposis syndrome.