Chapter 3 - Pathological Anatomy

Abstract

This chapter explains that a colonic diverticulum is a herniation of the mucosa through the muscular wall of the colon. The colonic wall consists of a mucous membrane of which the muscularis mucosa is a part, separated from the deep muscle layers by loose elastic connective tissue. The inner of the two muscle layers consists of fasciculi of circular fibers, which form a continuous tube around the bowel. It is mainly concentrated into three bands of taenia coli. In the sigmoid region, one of these lies at the mesocolic border of the colon and the other two are antimesocolic; all three are relatively broader in this region and so the interval among them is narrow. The three taenia fuse into one coat at the rectosigmoid junction that is usually around six inches above the peritoneal reflection. The most striking feature of the established diverticular disease is seen in the sigmoid colon. The muscle coat is greatly thickened and palpation reveals that often this thickening begins abruptly at the rectosigmoid junction and, above this point, the bowel is converted into a rigid tube with a narrowed lumen.