Colon polyps pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sadaf Sharfaei M.D.[2]
Overview
Any form of unregulated growth in the colon may cause polyps. The exact etiology is unclear. However, risk factors may contribute to the formation of polyps. There are four different types of polyps including inflammatory, hamartomatous, serrated, and adenomatous polyps, which have different pathogenesis. Inflammatory polyps are non-neoplastic polyps that occur following intestinal inflammation, infections, or ischemia. Hamartomatous polyp is an overgrowth of mature cells and connective tissue elements including smooth muscle, lamina propria, and cartilage, and fat. They are covered by a hypertrophic epithelium. Serrated polyps are different polyps which have variable malignant potential. They include hyperplastic, sessile serrated and traditional serrated polyps. Hyperplastic polyps are the most common polyps. Hyperplastic polyp is infolding of the crypt epithelium that forms serration or saw-toothed appearance. Sessile serrated polyps are flask-shaped crypts, with dilatation and branching but not pedunculated. Traditional serrated adenomas are serrated polyps that are protuberant and pedunculated, which are located in left colon.
Pathophysiology
Pathogenesis
- Any form of unregulated growth in the colon may cause polyps. The exact etiology is unclear. However, risk factors may contribute to the formation of polyps.
- There are four different types of polyps including inflammatory, hamartomatous, serrated, and adenomatous polyps, which have different pathogenesis.
- The pathophysiology of colon polyps depends on the histological type.
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Inflammatory polyps
- Inflammatory polyps are non-neoplastic polyps that occur following intestinal inflammation, infections, or ischemia.[1][2]
- They mostly occur in patients with inflammatory bowel disease, mainly ulcerative colitis.
- They are considered as pseudopolyps which contain inflammatory infiltrations with distorted mucosa.
- It had no malignant potential. However, it is recommended to biopsy the lesion and surrounding mucosa.
- Microscopic pathology of biopsy shows mixture of normal, ulcerated, and regenerating mucosa which is surrounded by areas of mucosal loss.
Hamartomatous polyps
- Hamartomatous polyp is an overgrowth of mature cells and connective tissue elements including smooth muscle, lamina propria, and cartilage, and fat. They are covered by a hypertrophic epithelium.[3]
- They might be pedunculated, inflamed, or smooth polyps which are solitary or multiple.
- Solitary hamartomatous polyps, also known as juvenile polyps, can present more commonly in younger population.
- Solitary polyps has no significant risk of cancer. However, multiple polyps of the colon have a 10% risk of malignancy.
Serrated polyps
- Serrated polyps are different polyps which have variable malignant potential. They include hyperplastic, sessile serrated and traditional serrated polyps. They have various histopathologies and manifestations.
- Hyperplastic polyps are the most common polyps.
- They are small outpouching, less than 5 mm, which are located mostly in rectosigmoid area.
- Hyperplastic polyp is infolding of the crypt epithelium that forms serration or saw-toothed appearance.
- The molecular basis of this transformation is still unclear. However, it has been attributed to failure of apoptosis.
- BRAF mutations are associated with crypt serration.
- There are three different subtypes of hyperplastic polyps based on degree of serration and content, including microvesicular type, goblet cell–rich type, and mucin-poor type.
- Sessile serrated polyps
- They are flask-shaped crypts, with dilatation and branching but not pedunculated.
- Crypts grow along muscularis mucosae and creating inverted T- or L-shaped appearance.
- Serration happens at the base and bottom of the crypts.
- Traditional serrated adenomas
- They are protuberant and pedunculated polyps, less than 1.5 cm, which are located in left colon.
- They have cytological dysplasia including nuclear transformation, irregular nuclear polarity, and serration.
- Cytological dysplasia causes crypts that are irregular and branching.
- Hyperplastic polyps are the most common polyps.
Adenomatous polyps
Genetics
- The development of colon polyps is the result of multiple genetic mutations.
- Genetic mutations might cause hereditary polyps disorders.
Familial adenomatous polyposis (FAP)
- FAP is due to mutations in the following genes:
- APC gene, which is located on chromosome 5 in band q21 or band q22 (5q21-q22)
- MUTYH gene, which is located on chromosome 1 between bands p34.2 and p32.1 (5p34.3-p32.1)
- MYH-associated polyposis (MAP) is caused by mutations in the MYH gene.
- It is thought that Peutz-Jeghers syndrome is the result of deletion or partial deletion of STK11 (LBK1) gene, located on chromosome 19p13.3.
- It is caused by mutation in the APC gene located in chromosome 5q21 (band q21 on chromosome 5).
Serrated polyposis syndrome
- They develop multiple serrated adenomatous polyps in the upper part of the colon.
Familial juvenile polyposis
- It is an autosomal dominant disorder.
- It increases risk of colorectal cancer
- It has extra-colonic tumors.
- There has been some association with the following genes:
- SMAD4 on chromosome 18
- PTEN on chromosome 10
Gross Pathology
- On gross pathology, outpouching, pedunculated or flat lesions are characteristic findings of colon polyps.
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Microscopic Pathology
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References
- ↑ Shussman, N.; Wexner, S. D. (2014). "Colorectal polyps and polyposis syndromes". Gastroenterology Report. 2 (1): 1–15. doi:10.1093/gastro/got041. ISSN 2052-0034.
- ↑ Li SC, Burgart L (2007). "Histopathology of serrated adenoma, its variants, and differentiation from conventional adenomatous and hyperplastic polyps". Arch. Pathol. Lab. Med. 131 (3): 440–5. doi:10.1043/1543-2165(2007)131[440:HOSAIV]2.0.CO;2. PMID 17516746.
- ↑ Zbuk KM, Eng C (2007). "Hamartomatous polyposis syndromes". Nat Clin Pract Gastroenterol Hepatol. 4 (9): 492–502. doi:10.1038/ncpgasthep0902. PMID 17768394.
- ↑ "File:Image of resected colon segment with cancer & 4 nearby polyps plus schematic of field defects with sub-clones.jpg - Wikimedia Commons".