Adenocarcinoma of Recto-Sigmoid
Gross Pathology: Almost 50% of all colorectal carcinomas arise in the rectosigmoid region. In older patients, proximal (right-sided) tumors are more frequent. About 3%-6% of tumors are multifocal. Grossly, colorectal carcinomas can be exophytic masses or deeply infiltrative ulcers. The exophytic lesions are more common in the proximal colon and they appear as a bulky polypoid mass with rolled edges that are clearly demarcated from the adjacent normal mucosa. Tumors in proximal colon rarely cause obstruction due to large caliber of cecum and ascending colon. In distal colon, the exophytic lesions tend to be annular and can cause “napkin-ring constriction” of the bowel lumen. The ulcerating infiltrative masses are not raised and may be flat or depressed than surrounding mucosa. Japanese authors have described flat or depressed variants of colorectal carcinoma that arise de novo. These tumors are capable of deep infiltration with lymphovascular invasion. Signet ring cell variants produce linitis plastic type appearance where the affected segment of colon shows diffuse firm thickening of the wall with narrowing of the passage. Rare examples may be associated with a polypoid mass. Mucinous variants of colorectal carcinoma have a gelatinous translucent appearance. Jelly-like material may be seen separating the layers of the bowel wall. The image shows a bulky tumor in the sigmoid colon. The anal mucosa can be seen to the right of the tumor.