Postgraduate Medicine

ISSN: 0032-5481 (Print) 1941-9260 (Online) Journal homepage:

Polyps in the colon John B. Marshall MD To cite this article: John B. Marshall MD (1992) Polyps in the colon, Postgraduate Medicine, 92:6, 53-65, DOI: 10.1080/00325481.1992.11701511 To link to this article:

Published online: 17 May 2016.

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Date: 12 June 2016, At: 03:05


First of three articles on diseases of the colon

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Polyps in the colon Answers to key questions

Preview Colorectal polyps are common in adults over age 40. With the oldest baby boomers now approaching their 50th birthday, medical practices are going to be full of patients with polyps. Will you be able to tell which polyps may become cancerous? In this article, Dr Marshall describes the differences between benign and malignant polyps, the protocols to follow for screening and treatment, and the latest advice on follow-up and prevention.

John B. Marshall, MD

What is an adenomatous polyp?

•!• Colo rectal polyps are visible protrusions from the mucosal surface of the bowel into the lumen. They can be neoplastic (eg, adenomatous polyps) or nonneoplastic (eg, hyperplastic polyps, hamartomatous polyps such as juvenile polyps and Peutz-Jeghers polyps, or inflammatory polyps). Medical interest in colorectal polyps results largely from the potential for malignant change in the adenomataus variety. This article addresses common and important questions about colorectal polyps and cancer.

Adenomas, common in adults over age 40, are benign neoplastic polyps. They have the potential for malignant change, which makes them clinically the most important variety of polyp. They are growths of dysplastic colorectal epithelium and may be pedunculated (ie, attached to the colon wall by a stalk) or sessile (ie, attached by a broad base). There are three histologic types of adenomas: • Tubular adenomas, the most common, accounting for at least two thirds of all colorectal adenomas

• Villous adenomas • Tubulovillous (mixed) adenomas Adenomas, like colon cancers, are distributed throughout the colon, although they have a mild predilection for distal areas (rectum and sigmoid colon). Nearly all colon cancers are believed to originate within previously benign adenomas.u The benign-tomalignant interval probably averages 10 to 15 years; intervals of less than 5 years are uncommon. Only some adenomas become malignant. The size and histologic type of the polyp are useful predictors of the likelihood of malignancy. Only 1o/o of polyps measuring less than 1 em in diameter contain cancer, compared with 1Oo/o of polyps measuring 1 to 2 em and 45% of polyps measuring more than 2 em. Malignant growth is found in up to 5% of tubular adenomas but in more than 40% of villous adenomas. This predilection of cancer for villous adenomas probably reflects the larger size of these polyps rather than any intrinsic malignant property. Can a polyp's histologic type

be determined by endoscopic appearance? Adenomatous and hyperplastic polyps make up the vast majority of colorectal polyps in adults.




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Doing a biopsy of a polyp larger than 1 em during a screening examination adds unnecessary expense, because total colonoscopy and polypectomy are necessary anyway.

Hyperplastic polyps are a proliferation of mature glandular cells that do not undergo malignant change. They are usually small and sessile, most measuring less than 5 mm. Although they may occur throughout the colon, hyperplastic polyps are much more commonly found in the rectum and sigmoid colon. If a polyp in an adult measures more than 1 em, it can safely be assumed to be an adenoma, since 97% of polyps of this size are. 3 For polyps less than 1 em, diagnosis (ie, adenomatous or hyperplastic) on the basis of endoscopy alone is not sufficiently accurate to be relied on, however, and biopsy is required, with one exception. Some diminutive (

Polyps in the colon. Answers to key questions.

Adenomatous polyps in the adult colon and rectum are of great clinical importance because they can undergo malignant degeneration. Size and histologic...
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