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Adenoma of Colon(Adenomatous Polyp)

Etiology:

Pathogenesis:

Epidemiology:

General Gross Description: • Colonic adenomas are localized proliferations of dysplastic epithelium which are initially flat, but with increased growth project from the mucosa forming polyps. • Adenomas are classified by their gross appearance as either sessile(flat) or pedunculated(having a stalk). • Small adenomas(•Pedunculated polyps are more likely to be tubular or tubulovillous histologic type and sessile lesions are more like villous adenomas • While it is impossible to predict the presence or absence of carcinoma based on the gross appearance of polyps, larger polyps have a higher incidence of concurrent malignancy than small polyps. Sessile polyps have a higher incidence of malignany than pedunculated polyps of the same size. • Sessile polyps are most common in the cecum and rectum while overall pedunculated polyps are equally split between the sigmoid-rectum, and the remainder of the colon.

General Microscopic Description: • By definition adenomas are composed of dysplastic epithelium. The nuclei are enlarged, cugar-shaped with an increase in nuclear chromatin, increased N/C ration, crowding and loss of polarity withing glands. There is often a decrease inmucous production. • Three subtypes of colonic adenomas are recognized: tubular; tubulovillous: and villous. • Villous adenomas have more than 50% of the dysplastic epithelium arranged in tall fingerlike villous projection similar to the villi seen in normal small intestinal mucosa. • Tubular adenomas have more than 75% of their epithelium arranged in tube like fashion which when cut accross looks like rows of transected gunbarrels. • Tubulovillous lesions have 25-50% villous component the rest being tubular. • Pedunculated adenomas are predominantly tubular with an increasing villous component as they grow larger. • Sessile adenomas are predominantly villous. • As a general rule, adenomas become more sessile as they become larger, and sessile lesions have a higher degree of dysplasia that tubular lesions.

Clinical Correlations: • Adenomas are benign lesions regardless of their degree of dysplasia. • The incidence of carcinoma within an adenoma is related to size, rare in adenomas less than 1cm and estimated at 40-50% in villous lesions >4cm.Adenomas with higher degrees of dysplasia have a higher incedence of carcinom. • The overall chance of developing carcinoma in a polyp is estimated at 5%. • Once a sporadic adenoma has developed, the cnace of a new polyp has been measured at 30% within 26 months. • Adenomas are generally asymptomatic, but a signicant number produce microscopic fecal blood loss.They are rarely large enough to cause obstructive signs in the absence of malignant change.

References: