Diverticulitis is an acute inflammatory process caused by bacterial proliferation within an existing colonic diverticulum. Epidemiology
Acquired diverticular disease of the colon has become an increasingly common disorder of industrialized nations. Diverticulosis coli was first described in the early 1700s by Littre but was not identified as a pathologic entity until the mid-nineteenth century by Cruveilhier. Radiologic studies have suggested that one-third of the population will have acquired the disease by age 50 and two-thirds by age 85. 21 Diverticula are rare in individuals under age 20.
Diverticulitis is estimated to occur in 10 to 25 percent of patients with known diverticulosis. The incidence of diverticulitis increases with age. Only 2 to 4 percent of patients with diverticulitis are under the age of 40. Diverticulitis in the younger age group tends to be a more virulent form of the disease, with frequent complications requiring earlier surgical intervention. 22 Although the frequency of the disease is higher in men, there is an increasing incidence of diverticulitis in women. Pathophysiology
Colonic diverticula are false diverticula because they do not include all layers of the bowel wall. They consist of mucosa and submucosa with a peritoneal covering that has herniated through a defect in the circular muscle layer of the wall. The sites of herniation are located between the mesenteric and antimesenteric taenia, where intramural blood vessels penetrate the muscularis.
A pathophysiologic mechanism to explain the development of diverticular disease is not apparent. It is still unresolved whether diverticular disease is a disorder of colonic motility, a colonic muscle abnormality, a connective tissue disorder, or a normal concomitant of aging. Low-residue diets have been implicated as a major factor in the pathogenesis of diverticular disease. The most common hypothesis is that acquired diverticula arise because of high intraluminal pressures in areas of relative weakness of the colonic wall. This is based upon observations that the majority of patients have diverticula located within the sigmoid colon. Laplace's law states that the tension on the wall of a hollow cylinder is inversely proportional to the radius of the cylinder multiplied by the pressure within the cylinder. This suggests that the intraluminal pressure in the colon is greatest where the lumen is narrowest. The diameter of the colon is smallest in the sigmoid region, and thus this region of the colon is the most likely location for the development of diverticula.
The complications of diverticular disease that bring the patient to the ED can be divided into two broad categories: (1) inflammation and its associated complications and (2) bleeding (see Chap, 70, "Gastrointestinal Bleeding").
Inflammation, or diverticulitis, is the most common complication of diverticular disease. It results when fecal material becomes inspissated in the neck of an acquired diverticulum, resulting in obstruction of the neck of the diverticulum and subsequent proliferation of colonic bacteria, mucous secretion, and distention of the diverticulum. Clinical diverticulitis always represents microperforation and inflammation of pericolonic tissue. Fortunately, fecal contamination of the peritoneum is usually limited because perforation of a diverticulum occurs into the leaves of the mesentery or because the contamination is walled off by the mobile loops of the sigmoid colon or small bowel and adjacent pelvic structures. Free perforation may occur with generalized peritonitis, but it is uncommon.
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