Distribution and significance of the smooth muscle component in polyps of the large intestine.

Immunocytochemical staining for alpha smooth muscle actin specifically reveals the distribution of the muscularis mucosae and pericryptal intramucosal smooth muscle fibers in the normal mucosa and polyps of the large intestine. In the latter, the muscular component is hyperplastic, especially in pedunculated polyps, which display a thick "muscular zone" at the top of the stalk. The diagnostic (and prognostic) significance of the distribution pattern of the muscular component in polyps, and in "early invasion" cases, is discussed.