Inflammatory Intestinal Disease

Sigmoid Diverticulitis

In general, diverticular disease refers to acquired pseudodiverticular outpouchings of the colonic mucosa and submucosa. Such colonic diverticula are rare in individuals younger than 30 years of age, but the prevalence approaches 50% in Western adult populations older than 60 years of age. Diverticula generally are multiple, and the condition is referred to as diverticulosis. This disease is much less common in developing countries, probably because of dietary differences.

Pathogenesis

Colonic diverticula tend to develop under conditions of elevated intraluminal pressure in the sigmoid colon. This is facilitated by the unique structure of the colonic muscularis propria, where nerves, arterial vasa recta, and their connective tissue sheaths penetrate the inner circular muscle coat to create discontinuities in the muscle wall. In other parts of the intestine, these gaps are reinforced by the external longitudinal layer of the muscularis propria, but in the colon, this muscle layer is discontinuous, being gathered into three bands termed taeniae coli. High luminal pressures may be generated by exaggerated peristaltic contractions, with spasmodic sequestration of bowel segments that may be exacerbated by diets low in fiber, which reduce stool bulk.

Morphology

Anatomically, colonic diverticula are small, flasklike outpouchings, usually 0.5 to 1 cm in diameter, that occur in a regular distribution in between the taeniae coli. They are most common in the sigmoid colon, but other regions of the colon may be affected. Colonic diverticula have a thin wall composed of a flattened or atrophic mucosa, compressed submucosa, and attenuated muscularis propria - often, this last component is totally absent. Obstruction of diverticula with stasis of contents, leads to inflammatory changes, producing diverticulitis and peridiverticulitis. Because the wall of the diverticulum is supported only by the muscularis mucosa and a thin layer of subserosal adipose tissue, inflammation, increased pressure, and mucosal ucleration within an obstructed diverticulum can readily result in perforation. With or without perforation, recurrent diverticulitis may cause segmental colitis, fibrotic thickening in and around the colonic wall, or stricture formation.

Clinical Features

Most individuals with diverticular disease remain asymptomatic throughout their lives. About 20% of those affected develop complaints including intermittent cramping, continuous lower abdominal discomfort, constipation, and diarrhea. Longitudinal studies have shown that while diverticula can regress early in their development they often become more numerous and larger over time. Whether a high-fiber diet prevents such progression or protects against diverticulitis is unclear. Even when diverticulitis occurs, it most often resolves spontaneously or after antibiotic treatment, and relatively few patients require surgical intervention.