Hyperplastic metaplastic polyps

The definition is a mucosal excrescence characterized by elongated, serrated crypts lined by proliferative epithelium in the bases with infolded epithelial tufts and enlarged goblet cells in the upper crypts and on the luminal surface, imparting a saw-tooth outline. In the appendix, diffuse hyperplasia may occur as a sessile mucosal proliferation. The epithelial nuclei in the serrated region are small, regular, round and located at

Fig.6.27 Tubular adenoma of colon.
Fig. 6.28 Tubulovillous adenoma, partly sessile, partly pedunculated.

Fig. 6.29 A Adenoma with low-grade dysplasia and well-maintained glandular architecture. B Low-grade dysplasia with regular but slightly elongated, hyperchromatic nuclei. Cytoplasmic mucin is retained.

the base of the cells adjoining the basement membrane, which is often thickened beneath the surface epithelial cells. The cytoplasm contains prominent mucin vacuoles, which are usually larger than normal goblet cells. The proliferative zone often shows increased cellularity and mitotic activity, which can be mistaken for adenoma. Hyperplastic polyps are traditionally considered non-neoplastic, but ras mutation is common, clonality has been demonstrated, and biochemical abnormalities and epidemiological associations that occur in colorectal adenomas and carcinomas have been found {851, 663, 1178}. These lines of evidence suggest that hyperplastic polyps may be neoplastic but have a molecular patho-genesis that differs from the adenoma-adenocarcinoma sequence due to absence of inactivation of the APC/beta-catenin pathway.

Juvenile polyps

Sporadic juvenile polyps are typically spherical, lobulated and pedunculated and considered hamartomatous. They most commonly occur in children. The surface is often eroded and friable, and the cut surface typically shows mucin-containing cysts. On histology, the abundant stroma is composed of inflamed,

often oedematous granulation tissue that surrounds cystically dilated glands containing mucin. The glands are lined by cuboidal to columnar epithelial cells with reactive changes. The juvenile polyps in patients with juvenile polyposis syndrome may have the macroscopic and microscopic appearances of sporadic juvenile polyps, but they often have a frond-like growth pattern with less stroma, fewer dilated glands and more proliferated small glands (microtubular pattern) than their sporadic counterparts. Intraepithelial neoplasia (dysplasia) is rare in sporadic juvenile polyps. Intra-epithelial neoplasia in this setting results from inactivation of the APC/beta-catenin pathway analogous to the genetic basis of adenoma formation {2145}.

Peutz-Jeghers polyps

These are discussed in the small intestine section.

Reactive lesions

Inflammatory polyps. These non-neoplas-tic polyps are composed of varying proportions of reactive epithelium, inflamed granulation tissue and fibrous tissue, often with morphological similarity to juvenile polyps; inflammatory polyps are seen in a variety of chronic inflammatory diseases including chronic inflammatory bowel disease and diverticulitis. Lymphoid polyps. These result from aggregates of reactive mucosa-associat-ed lymphoid tissue with conspicuous germinal centres located in the mucosa and/or submucosa.

Mucosal prolapse. On occasion, mucos-al prolapse can produce morphological features that mimic neoplasia, including polyps, masses and ulcers characterized histologically by elongated, distorted, regenerative glands surrounded by a proliferation of smooth muscle fibres from the muscularis mucosae, together with superficial erosions, inflamed granulation tissue and fibrosis {159}. Widening of gland lumina at the surface is common. Examples of this phenomenon include inflammatory cloacogenic polyp {1083}, solitary rectal ulcer and cap polyp. The process can extend into the bowel wall, producing colitis cystica profunda.

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