Pie chart of colorectal polyp etiologies

A hyperplastic polyp is a type of gastric polyp or colorectal polyp.

Cancer risk

Most hyperplastic polyps are found in the distal colon and

rectum The rectum (: rectums or recta) is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. Before expulsion through the anus or cloaca, the rectum stores the feces temporarily. The adult ...

. They have no malignant potential, which means that they are no more likely than normal tissue to eventually become a cancer. Hyperplastic polyps on the right side of the colon do exhibit a malignant potential. This occurs through multiple mutations that affect the DNA-mismatch-repair pathways. As such DNA mutations during replication are not repaired. This leads to microsatellite instability which can eventually lead to malignant transformation in polyps on the right side of the colon.

Serrated polyposis syndrome

''Serrated polyposis syndrome'' is a rare condition that has been defined by the

World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...

as either: :#≥5 serrated lesions/polyps proximal to the rectum, all ≥ 5 mm in size, with two lesions ≥10 mm :#>20 serrated lesions/polyps of any size distributed throughout the large bowel with 5 proximal to the rectum.

Histopathology

Histopathologically, there are two main types of hyperplastic polyps, which have genetic differences, as well as different histologic structure, but no significant differences clinically. The two main types of hyperplastic polyps are microvesicular

mucin Mucins () are a family of high molecular weight, heavily glycosylated proteins ( glycoconjugates) produced by epithelial tissues in most animals. Mucins' key characteristic is their ability to form gels; therefore they are a key component in ...

-rich type and

goblet cell Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin 2 in the lower gastrointestinal tract, and mucin 5AC in the respiratory tract. The goblet cells mainly use the merocrine method of secretion, secre ...

-rich type. A mucin-poor type with eosinophilic cytoplasm, which is rare, was previously described. However, the mucin poor type is no longer considered a distinct subtype.

Mucin-rich type

The luminal portion has a serrated ("saw tooth") appearance formed by tufts or folds of abundant apical cytoplasm. It contains glands with star-shaped lumina. Last updated 6/2/2015 There are crypts that are elongated but straight, narrow and hyperchromatic at the base. All crypts reach to the

muscularis mucosae The muscularis mucosae (or lamina muscularis mucosae) is a thin layer ( lamina) of muscle of the gastrointestinal tract, located outside the lamina propria, and separating it from the submucosa. It is present in a continuous fashion from the esop ...

. The

basement membrane The basement membrane, also known as base membrane, is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tis ...

is frequently thickened.

Goblet cell-rich type

Elongated, fat crypts and little to no serration. Therefore, they may not be obvious without comparing to adjacent normal intestinal wall. They are filled with goblet cells, extending to surface, which commonly has a tufted appearance.

Epithelial misplacement

Infrequently, the epithelium is misplaced into the submucosa. Such polyps are termed "inverted hyperplastic polyps". They appear to be restricted to the sigmoid colon and

. The misplaced epithelium is mucin-depleted, similar to the basal one-third of the polyp. The misplacement is accompanied by the

lamina propria The lamina propria is a thin layer of connective tissue that forms part of the moist linings known as mucous membranes or mucosae, which line various tubes in the body, such as the respiratory tract, the gastrointestinal tract, and the urogenital ...

and is continuous with the overlying polyp through a gap in the

. It may require slices at multiple levels to demonstrate microscopically. In such cases adjacent bleeding and hemosiderin deposition is common. Collagen type IV stain will have a strong continuous staining around nests.

Cellular structure

Nuclei are small, regular, round and basal in the luminal half of the crypts, most reliably evaluated near the luminal surface. There are proliferative changes at the base of crypts, where nuclei are enlarged, the nucleus/cytoplasm ratio is elevated.

Immunohistochemistry

Immunohistochemistry Immunohistochemistry is a form of immunostaining. It involves the process of selectively identifying antigens in cells and tissue, by exploiting the principle of Antibody, antibodies binding specifically to antigens in biological tissues. Alber ...

using Ki-67 stains the basal to of crypts, indicating a proliferative zone. CK20 is positive in the luminal or parts.

Differential diagnoses

Non-proliferative versus proliferative colonic crypts

The deep proliferative zones and reactive processes closely mimic changes seen in colorectal adenomas. Features that distinguish a hyperplastic polyp from a tubular colorectal adenoma are as follows: A sessile serrated adenoma or traditional serrated adenoma is suspected if there is either of the following: * Nuclear stratification * Loss of polarity * Dysplasia A sessile serrated adenoma is suspected in case of any of the following: * Size ≥0.5 cm * Location in right colon If both are present, it is almost always an SSA. Other features causing a suspicion for sessile serrated adenoma are: * Dilation of crypts * Branching of crypts * Horizontal glands at the base * Mature mucinous cells at the base of crypts

References

{{Digestive system neoplasia Digestive system neoplasia Large intestine Anatomical pathology