Pathogenesis of colonic diverticulitis and diverticulosis.

Colonic diverticula result from herniation of the mucosa through weak spots in the muscular wall. Clinically manifested diverticulitis has been thought to have its pathologic basis in an abscessed diverticulum obstructed by a fecalith, but studies of resected sigmoids have failed to produce evidence to support this view. Instead, the outstanding lesion was found to be a perforation in the fundus of a diverticulum, with surrounding peridiverticular or pericolic inflammation. Another surprising finding in pathologic studies was that one out of three sigmoids resected for "diverticulitis" showed no inflammation in or around the diverticula, but the wall of the sigmoid was impressively thickened. This type of diverticulosis, which is frequently symptomatic, has been referred to as painful diverticular disease or spastic colon diverticulosis. Diverticula without muscle thickening are usually asymptomatic, and the condition is referred to as diverticulosis or simple massed diverticulosis. It is uncertain whether the two types have a similar pathogenesis. High intrasigmoid pressures, abnormalities of sigmoid musculature, low-fiber diet, and psychologic stress are thought to be important factors in the formation of diverticula.