COLON (Robbins pp 827)

Adenomas (Robbins pp 828)

An adenomatous polyp occurs due to dysplastic proliferation of epithelial cells. There are three main types of adenomas: 1) Tubular, 2) Villous, 3) Tubulovillous.

Tubular (60%): This means the histological nature of the glands is tubular. Small lesions may be sessile, while large ones may have a stalk. The stalk is composed of fibromuscular tissue, surrounded by normal colonic mucosa. The epithelium of the adenoma itself (i.e.: the cauliflower like structure at the end of the stalk) is dysplastic.

Villous (10%): The villi present in the colon are covered with dysplastic epithelium that project into the lumen. The adenoma is sessile.

Tubulovillous (25%): These types of adenoma have areas where the polyp has a stalk and where it is villous.

All adenomatous polyps cause a four fold greater risk of colorectal cancer.

General rules:

1) Tubular adenomas are small and pedunculated,

2) Villous adenomas are large and sessile,

3) Malignancy of an adenoma depends on: a) polyp size (>4cm or <4cm),>

Polyposis syndromes (Robbins pp 831)

All of these syndromes are autosomal dominant, and they are important because they can transform into carcinomas.

FAP (polyposis coli): The defect is in the APC gene in chromosome 5 (q21-22 region). Hundreds of tubular adenomas line the colonic mucosa. Have nearly 100% Ca transformation rate.

Gardner’s syndrome: This is just a variation of FAP. You get multiple adenomatous polyps + osteomas (mandible, skull, long bones).

Turcot’s syndrome: This is another variant. You get multiple adenomatous polyps + CNS neoplasms (mainly gliomas).

Juvenile polyposis: Ca risk is low – 15%.

Category: Pathology Notes