Pseudo-carcinomatous invasion in adenomatous polyps of the colon and rectum.

The histology of pseudo-carcinomatous invasion in adenomatous polyps of the colon and rectum is described and the appearances are contrasted with those seen in malignant polyps. The recognition of pseudo-carcinomatous invasion is important in the differential diagnosis of benign and malignant polyps of the large bowel. Failure to distinguish it from carcinoma may lead to wrong treatment and false reports of the incidence and prognosis of cancer of the colon and rectum. The evidence suggests that pseudo-carcinomatous invasion may be the result of repeated twisting of the stalk of a polyp which causes haemorrhage and this facilitates the passage of non-malignant adenomatous epithelium through the muscularis mucosae.