Diverticular Disease

Diverticula are small pouches of mucosa and submucosa that herniate outward through the muscular wall of the colon. They are false diverticula — they contain only the inner layers, not the full thickness of the bowel wall, which is why they are thin-walled and prone to perforate.

They form at the points where the wall is structurally weakest: the sites where the vasa recta, the small arteries supplying the colon, penetrate the circular muscle layer. Raised intraluminal pressure pushes mucosa out through these gaps. The sigmoid colon is affected in the great majority of Western cases because it has the smallest diameter and therefore, by Laplace’s law, the highest wall tension for a given pressure.

The terms matter and are often confused:

• Diverticulosis — diverticula are present, with no symptoms. Common and largely age-related.
• Diverticular disease — diverticula causing symptoms.
• Diverticulitis — inflammation or infection of one or more diverticula, from micro-perforation of the thin pouch wall.

Prevalence rises steeply with age, affecting a majority of people over 70 in Western populations, and is strongly associated with a low-fibre diet — the traditional explanation being that low stool bulk requires higher segmental pressures to propel. Obesity, physical inactivity, smoking, and regular NSAID use are further associations, the last particularly with perforation and bleeding. The distribution differs geographically: right-sided diverticula predominate in East Asian populations.

Diverticulosis is asymptomatic and usually an incidental finding on colonoscopy or CT.

Symptomatic diverticular disease causes intermittent left lower quadrant pain, often colicky and eased by passing stool or wind, with bloating and erratic bowel habit. It overlaps closely with irritable bowel syndrome.

Acute diverticulitis presents with constant left lower quadrant pain, fever, and localized tenderness — sometimes described as left-sided appendicitis. Nausea, anorexia and a change in bowel habit are common; a tender mass may be palpable. Peritonism, guarding and rigidity signal perforation.

Diverticular bleeding is a separate presentation and usually painless: sudden, brisk, dark red or maroon rectal bleeding from erosion of a vasa recta at the neck of a diverticulum. It is a leading cause of major lower gastrointestinal haemorrhage and stops spontaneously in most cases.

Perforation may be contained, forming a pericolic or pelvic abscess, or free, causing purulent or faeculent peritonitis — a surgical emergency. Repeated inflammation produces fibrosis and stricture, with obstructive symptoms. Fistulae may form to adjacent organs, most commonly the bladder: a colovesical fistula presents with pneumaturia and faecaluria and is characteristic enough to be diagnostic.

Acute diverticulitis is suggested clinically by left lower quadrant pain with fever and raised inflammatory markers. CT with contrast is the investigation of choice: it confirms the diagnosis, distinguishes uncomplicated from complicated disease, and identifies abscess, perforation and fistula — which determines management.

Colonoscopy is avoided in the acute phase because of perforation risk, but is recommended six to eight weeks after an episode to exclude a colorectal carcinoma, which can present identically. A full blood count and CRP support the diagnosis and track response; urinalysis may show sterile pyuria where inflamed bowel lies against the bladder.