Perforated sigmoid diverticulitis and their abscesses often resolve spontaneously. However, large or unresolving abscesses may require percutaneous drainage under ultrasound or CT guidance. Perforation of a diverticular abscess into the peritoneal cavity will result in purulent peritonitis with localized tenderness becoming generalised peritonism.

The localized inflammatory process associated with a diverticulum may perforate through another epithelial surface to form a fistula. The commonest type of fistula associated with diverticular disease is a colovesical fistula resulting from perforation of a diverticulum into the bladder. Patients with colovesical fistulae may present without bowel symptoms but with recurrent urinary tract infections and/or pneumaturia.

Fistulation can occur into other organs, such as the vagina or small intestine, and occasionally enterocutaneous fistulae may occur.

Generalized peritonitis associated with diverticular disease is due to the presence of free pus, faeces, or both, within the peritoneal cavity. Faecal peritonitis occurs where there has been necrosis of the intestinal wall resulting in the leakage of faeces into the peritoneal cavity. Patients are often gravely ill with marked peritonism and septic shock.

Bleeding sometimes occurs from vessels at the neck of a diverticulum and tends to be profuse – such blood loss usually arises from a single diverticulum, most frequently situated in the right colon.

Diverticular disease cannot be held responsible for occult lower gastrointestinal bleeding leading to an iron deficiency anaemia; in these situations other causes should be sought, such as neoplasia or angiodysplasia.

Inflammatory changes with associated scarring from previous episodes of acute diverticulitis and smooth muscle hypertrophy may be sufficient to cause a complete blockage of the colonic lumen and precipitate acute large bowel obstruction. Incomplete obstruction resulting from scarring may result in a variable bowel habit and intermittent colicky abdominal pain. Stricturing as a result of diverticular disease can be indistinguishable from malignancy on radiological investigation.

Diverticulosis is detected readily by both barium enema and contrast enhanced computed tomography (CT). Double contrast barium enema will demonstrate diverticulae, any strictures present and may also be helpful in demonstrating the presence of fistulae.

In areas of severe diverticulosis it may be impossible to safely exclude small polyps or carcinomas, and a colonoscopy or flexible sigmoidoscopy is indicated if doubt exists. Double contrast barium enema is deferred in the presence of acute diverticulitis and is usually performed 4-6 weeks after the acute episode has settled.

In acute situations other imaging modalities such as CT and/or ultrasound scanning provide the mainstay of investigation.

Colonoscopy is easily performed as an outpatient procedure. It clearly demonstrates the presence of diverticulae and any other mucosal abnormalities. It is the procedure of choice when patients present with rectal bleeding or where a barium enema has failed to adequately delineate an area of the colon. Colonoscopy, however, may be difficult in the presence of extensive diverticular disease due to spasm, rigidity and the presence of the diverticulae themselves.

Computerised tomography and ultrasound scanning Contrast enhanced CT scanning is the investigation of choice in patients with acute diverticultis when the characteristic colonic wall thickening with inflammation of pericolic fat are frequently seen. In complicated cases, abscesses, extraluminal gas and extraluminal contrast may all be detected by CT scanning. Drainage of intra- abdominal abscesses under CT guidance is practiced in many units and can prevent the need for operative intervention in the acute setting. Ultrasound scanning, although less sensitive, can also demonstrate wall thickening and the presence of significant abscesses.