35 - Diverticulitis

Diverticula are thought to arise from defects in the muscularis layer of the intestines (Fig. 35.1) and are related to abnormalities in muscle tone and increased intraluminal pressure; saclike protrusions eventually form at points of weakness. If stool is caught in these sacs, it becomes inspissated and hardened and causes abrasions of the mucosa that lead to inflammation, although the same end result can occur from pressure differentials alone without the presence of trapped fecal material. Diverticula generally form at a site of focal weakness in the wall of the bowel, such as the location of blood vessel penetration (vasa recta). The mucosal and submucosal layers herniate through the muscular layer of the intestine, with only a covering of serosa remaining. This leads to an inherent weakness in the diverticular sac relative to the normal bowel. Only thinned layers of mucosa protect blood vessels, which are subject to stretching and thinning of their media, thereby predisposing to weakness and rupture of the vascular tissue. The left side of the colon is the most common site for diverticulosis in patients with westernized diets and lifestyle. Right-sided diverticula occur more frequently in certain Asian populations. Right-sided diverticula have a higher rate of hemorrhage because of anatomic differences in their development. Small bowel diverticula occur most commonly in the duodenum, where they are predominantly asymptomatic. About 20% of small bowel diverticula occur in the jejunum or ileum; complications develop in these diverticula at rates three times greater than in duodenal diverticula. A low-fiber diet and constipation may contribute to the development of diverticular disease. High-fiber diets that prevent constipation clearly lead to fewer relapses of diverticulitis and less frequent complications. Lack of physical activity and advanced age are both believed to increase the incidence of the disease. Men and women are affected equally.