Criteria
Histologic features
In normal colorectal mucosa, cellular proliferation is limited to the lower half of the tubule and cellular maturation, and differentiation takes place from the base of the crypt up to the mucosal surface. In adenomatous polyps, this proliferation is not limited to the base of the tubules, and the differentiation of cells is absent, leading to dysplasia.
Low-grade dysplasia represents tissue in which tubules are lined throughout their length by cells similar to those found at the base of the crypt in normal mucosa: with slightly enlarged, hyperchromatic, and oval-shaped nuclei with normal orientation.
In moderate dysplasia these features are more pronounced, with more mitotic figures, less cellular polarity, and more crowded glands.
In severe dysplasia these features are once again more pronounced, with large, dark nuclei, increased nuclear to cytoplasmic ratio, cellular pleomorphism, and disordered glands and tubules. The dysplasia is confined to the muscularis mucosae and more superficial layers and is in this way distinguished from invasive carcinoma.
Endoscopic features: Kudo Pit Pattern classification[44]
Under magnification, the colonic mucosa can be seen to have a pattern of pits marking its surface. Using advanced endoscopic techniques, these pit patterns can be visualized and the polyp can be classified.
Types I and II are benign and show regular round or star-shaped pits
Types III to V are malignant and are more disordered and chaotic, with different sizes and more tubular and irregular pits.
Risk of colorectal cancer after polypectomy[45]
Patients with adenomas who have had a polypectomy are at high risk of developing future colorectal cancer if they have:
≥2 premalignant polyps, including at least 1 advanced colorectal polyp (a serrated polyp ≥10 mm containing any grade of dysplasia, or an adenoma ≥10 mm or containing high-grade dysplasia); or
≥5 premalignant polyps.
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