{{short description|Type of colorectal polyp}} {{Lead too short|date=October 2019}} {{Infobox medical condition (new) | name = Hyperplastic polyp | synonyms = | image = Hyperplastic Polyp of the Rectum (14060044206).jpg | width = | alt = | caption = Micrograph of hyperplastic polyp | pronounce = | specialty = Gastroenterology | symptoms = Usually asymptomatic | complications = Colorectal cancer | onset = | duration = | types = Microvesicular type<ref name=Crockett/><br/>Goblet cell–rich type<ref name=Crockett/> | causes = | risks = | diagnosis = Colonoscopy | differential = Colorectal adenoma, Traditional serrated adenoma | prevention = | treatment = | medication = | prognosis = | frequency = | deaths = }} thumb|250px|Incidences and malignancy risks of various types of colorectal polyps, with hyperplastic polyps at bottom left. 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.<ref name="Robbins polyps">{{cite book|last=Kumar|first=Vinay|title=Robbins and Cotran pathologic basis of disease.|year=2010|publisher=Saunders/Elsevier|location=Philadelphia, PA|isbn=978-1-4160-3121-5|edition=8th|chapter=17 - Polyps|url=http://www.mdconsult.com/books/page.do?eid=4-u1.0-B978-1-4377-0792-2..50022-5--cesec238&isbn=978-1-4377-0792-2&uniqId=278090687-4#4-u1.0-B978-1-4377-0792-2..50022-5--f46}}</ref> They have no malignant potential,<ref name="Robbins polyps" /> which means that they are no more likely than normal tissue to eventually become a cancer.{{citation needed|date=August 2020}}
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.{{citation needed|date=August 2020}}
==Serrated polyposis syndrome== {{Main|Serrated polyposis syndrome}} ''Serrated polyposis syndrome'' is a rare condition that has been defined by the World Health Organization as either:<ref name=Dekker>{{cite journal |last1=Dekker |first1=E |last2=Bleijenberg |first2=A |last3=Balaguer |first3=F |last4=Dutch-Spanish-British Serrated Polyposis Syndrome |first4=collaboration. |title=Update on the World Health Organization Criteria for Diagnosis of Serrated Polyposis Syndrome. |journal=Gastroenterology |date=May 2020 |volume=158 |issue=6 |pages=1520–1523 |doi=10.1053/j.gastro.2019.11.310 |pmid=31982410|doi-access=free }}</ref> :#≥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.<ref name=Stanford/> The two main types of hyperplastic polyps are microvesicular mucin-rich type and goblet cell-rich type.<ref name=Crockett>{{cite journal |last1=Crockett |first1=SD |last2=Nagtegaal |first2=ID |title=Terminology, Molecular Features, Epidemiology, and Management of Serrated Colorectal Neoplasia. |journal=Gastroenterology |date=October 2019 |volume=157 |issue=4 |pages=949–966.e4 |doi=10.1053/j.gastro.2019.06.041 |pmid=31323292|doi-access=free }}</ref> A mucin-poor type with eosinophilic cytoplasm, which is rare, was previously described.<ref name=Stanford/> However, the mucin poor type is no longer considered a distinct subtype.<ref name=Crockett />
===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.<ref name=Stanford>{{cite web|url=http://surgpathcriteria.stanford.edu/gitumors/colorectal-hyperplastic-polyp/|title=Hyperplastic Polyp of the Colon and Rectum|author=Robert V Rouse|website=Stanford University School of Medicine|date=2010-01-31|access-date=2019-09-27|archive-date=2019-12-11|archive-url=https://web.archive.org/web/20191211031701/http://surgpathcriteria.stanford.edu/gitumors/colorectal-hyperplastic-polyp/|url-status=dead}} Last updated 6/2/2015</ref> There are crypts that are elongated but straight, narrow and hyperchromatic at the base. All crypts reach to the muscularis mucosae.<ref name=Stanford/> The basement membrane is frequently thickened.<ref name=Stanford/>
===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.<ref name=Stanford/>
They are filled with goblet cells, extending to surface, which commonly has a tufted appearance.<ref name=Stanford/>
===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 rectum. The misplaced epithelium is mucin-depleted, similar to the basal one-third of the polyp. The misplacement is accompanied by the lamina propria and is continuous with the overlying polyp through a gap in the muscularis mucosae. It may require slices at multiple levels to demonstrate microscopically.<ref name=Stanford/>
In such cases adjacent bleeding and hemosiderin deposition is common. Collagen type IV stain will have a strong continuous staining around nests.<ref name=Stanford/>
===Cellular structure=== Nuclei are small, regular, round, and basal in the luminal half of the crypts, most reliably evaluated near the luminal surface.<ref name=Stanford/>
There are proliferative changes at the base of crypts, where nuclei are enlarged, the {{sfrac| nucleus |  cytoplasm  }} ratio is elevated.<ref name=Stanford/>
===Immunohistochemistry=== Immunohistochemistry using Ki-67 stains the basal {{sfrac|  1  | 3 }} to {{sfrac|  1  | 2 }} of crypts, indicating a proliferative zone.<ref name=Stanford/>
CK20 is positive in the luminal {{nobr| {{sfrac|  1  | 2 }} ~ {{sfrac|  2  | 3 }} parts.<ref name=Stanford/>}}
===Differential diagnoses=== [[File:Non-proliferative versus proliferative colonic crypts.jpg|thumb|Non-proliferative (left) versus proliferative (large at right) colonic crypts, where the latter's proximity to the surface confers a diagnosis of a tubular colorectal adenoma.]] The deep proliferative zones and reactive processes closely mimic changes seen in colorectal adenomas.<ref name=Stanford/>
Features that distinguish a hyperplastic polyp from a tubular colorectal adenoma are as follows: {|class="wikitable" ! Hyperplastic Polyp<ref name=Stanford/> !! Tubular Adenoma<ref name=Stanford/> |- | Nu dysplasia || Dysplasia |- | Proliferative epithelium restricted to base|| Proliferative epithelium present at the surface |- | Gland lining cells mature at the surface || No surface maturation |}
A sessile serrated adenoma or traditional serrated adenoma is suspected if there is either of the following:<ref name=Stanford/> * Nuclear stratification * Loss of polarity * Dysplasia
A sessile serrated adenoma is suspected in case of any of the following:<ref name=Stanford/> * 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:<ref name=Stanford/> * Dilation of crypts * Branching of crypts * Horizontal glands at the base * Mature mucinous cells at the base of crypts
==References== {{reflist|25em}}
{{Digestive system neoplasia}}
Category:Digestive system neoplasia Category:Large intestine Category:Anatomical pathology