Increasing age is associated with the development of pulsion diverticula of the colon. This process is associated with consumption of a diet low in roughage. Each diverticulum consists of a mucosal pouch with no external muscle. Diverticula are most commonly present in the sigmoid colon. They occur with decreasing frequency from sigmoid colon to caecum. They do not occur in the rectum, which has a complete outer longitudinal layer of muscularis propria. There may be hypertrophy of the muscularis propria of the sigmoid colon.
Uncomplicated diverticular disease is usually asymptomatic. Treatment of patients with diverticular disease with a long-term high-roughage diet reduces the incidence of the complications of diverticular disease. The infective complications of diverticular disease (acute diverticulitis, abscess, perforation and fistula formation) result when the neck of a diverticulum, which is narrower than the sac, becomes obstructed by faecal material and the contents of the sac become infected.
Complications of diverticular disease
The complications of diverticular disease include colovesical fistula, colovaginal fistula, coloenteric fistula, small bowel obstruction (discussed above under ‘Acute abdominal colic’), large bowel obstruction (discussed above under ‘Acute abdominal colic’) and gastrointestinal bleeding.
The outstanding presenting feature of a colovesical fistula is pneumaturia (passage of gas with urine) or faecuria (which is less common). There may be hypogastric pain due to associated urinary bladder inflammation. The fistula is usually the size of a pinhole. It is unusual to be able to demonstrate the fistula with either a barium enema or cystogram. CT scanning will often demonstrate an inflammatory mass of the colon adjacent to the bladder, with a variable amount of free gas seen within the bladder lumen. This is indicative of the presence of a fistula but the site of the fistula often cannot be determined.
The outstanding presenting feature of a colovaginal fistula is a feculent vaginal discharge. A previous hysterectomy has usually been performed as this allows the segment of sigmoid colon to come into contact with the apex of the vagina.
The outstanding presenting feature of a coloenteric fistula is profuse diarrhoea and significant weight loss. The treatment of all fistulae is resection of the affected segment of colon and oversewing the defect in the bladder or vagina, or resection of the affected segment of small bowel.