Which polyp has maximum malignant potential ?

Ans. is 'a' i.e., Sessile Polyp --> Polyp is a grossly visible protrusion from the mucosal surface and it is classified pathologically as. a) Adenomatous polyp b) Juvenile polyp (hamaomatous polyps) c) Inflammatory polyp d) Hyper plastic polyp (hyperplastic mucosal proliferation) Adenomatous polyps These are premalignant lesions. The risk of malignant degeneration is related to both the size and type of polyp. Majority of colorectal carcinomas evolve from adenomatous polyps; this sequence of events is the adenoma-carcinoma sequence. Hamaomatous Polyps (Juvenile Polyps) In contrast to adenomatous polyps, hamaomatous polyps (juvenile polyps) are not usually premalignant. These lesions are the characteristic polyps of childhood but may occur at any age. Inflammatory Polyps (Pseudopolyps) Inflammatory polyps occur most commonly in the context of inflammatory bowel disease, but may also occur after amebic colitis, ischemic colitis, and schistosomal colitis. These lesions are not premalignant. Hyperplastic Polyps Hyperplastic polyps are the most common colonic polyps, but they are usually quite small (Ninety percent of these polyps are less than 3 mm in size) These lesions are not premalignant. Adenomatous polyps have special clinical significance because only adenomatous polyps are clearly premalignant, and only a minority of these adenomatous lesions ever develop into a cancer. Clinically, the probability of an adenomatous polyp becoming a cancer depends on three factors 1) Gross appearance of the lesion --> on gross appearance polyps are of two types a) Pedunculated (stalked) b) Sessile (flat based) Cancer develops more frequently in sessile polyps. 2) Histologically --> Histologically polyps are of 3 types a) Tubular b) Villous (papillary) c) Tubulovillous Out of these histological types villous adenomas which are usually sessile become malignant more than 3 times as often as tubular adenomas.