Define Diverticular Disease. Describe its pathogenesis, clinical features and complications.

The Concept & Terminology

A diverticulum of the colon is an outpouching of mucosa and submucosa herniating through the muscular wall — a 'false' diverticulum (it lacks the muscle layer), in contrast to a 'true' diverticulum containing all layers. It is important to separate the terms: diverticulosis is the mere presence of diverticula (often asymptomatic), diverticular disease is when they cause symptoms, and diverticulitis is inflammation of a diverticulum.

Pathogenesis — a Disease of Low Fibre

The mechanism explains the site and the epidemiology. A low-fibre diet produces small, hard stools that require high segmental intraluminal pressures to propel. This pressure forces the mucosa to herniate through the weakest points of the colonic wall — where the blood vessels (vasa recta) penetrate the muscle. The sigmoid colon, having the smallest calibre and highest pressures, is by far the commonest site, and this is why the disease is common in low-fibre Western populations.

Clinical Features

Most diverticulosis is asymptomatic, discovered incidentally. Symptomatic diverticular disease causes left iliac fossa pain, altered bowel habit and bloating. Acute diverticulitis presents with left iliac fossa pain, fever and localised tenderness — earning it the label 'left-sided appendicitis' — often with a raised white cell count and CRP.

Complications

The complications are high-yield because they are the reason diverticular disease needs surgery:

• Perforation — leading to a localised abscess or generalised (purulent or faeculent) peritonitis.
• Haemorrhage — a common cause of brisk, painless lower gastrointestinal bleeding (an eroded vasa recta).
• Fistula — most classically a colovesical fistula, presenting with pneumaturia and faecaluria and recurrent urinary infections; also colovaginal.
• Stricture — from repeated inflammation, causing large-bowel obstruction.
• Abscess formation.

Investigation & Management

CT is the investigation of choice in acute diverticulitis (it confirms the diagnosis, detects abscess/perforation, and allows the Hinchey classification). Colonoscopy is performed after an acute episode settles — not during it, because of the perforation risk — mainly to exclude a carcinoma. Management is graded:

• Uncomplicated diverticulitis — antibiotics, bowel rest and analgesia, with a long-term high-fibre diet.
• Abscess — radiologically guided drainage.
• Perforation with peritonitis — emergency surgery, classically Hartmann's procedure (resection of the diseased sigmoid with an end colostomy and closure of the rectal stump).
• Fistula or stricture — elective resection.

Hinchey Classification & Decisions

The Hinchey classification grades the severity of perforated diverticulitis and guides management: stage I (a small pericolic abscess) and II (a larger pelvic abscess) can often be managed with antibiotics and radiological drainage, whereas stage III (purulent peritonitis) and IV (faeculent peritonitis) require emergency surgery. This staged approach explains why not every perforation goes straight to theatre, and matches the intervention to the disease.

The Mimic of Carcinoma

A recurring clinical theme is that diverticular disease and colonic carcinoma can be indistinguishable — both can cause a stricture, altered bowel habit, bleeding or a mass in the sigmoid of an older patient. This is precisely why a colonoscopy is performed once an acute episode settles: to be sure a 'diverticular' stricture is not actually a cancer. Failing to exclude malignancy is the classic error in managing left-sided colonic disease.

Management Principles & the Bottom Line

Modern management is increasingly conservative: many episodes of uncomplicated diverticulitis settle with antibiotics (and some mild cases without them), reserving surgery for complications or recurrent disabling disease. The bottom line is a low-fibre, high-pressure sigmoid that inflames ('left-sided appendicitis') and, when it complicates, does so by perforation, bleeding, fistula or stricture — with Hartmann's procedure the emergency operation for faeculent peritonitis.

• CT is the investigation of choice in acute diverticulitis (Hinchey classification); colonoscopy after it settles (exclude cancer).
• Perforated diverticulitis with peritonitis → Hartmann's procedure (resection + end colostomy).
• Colovesical fistula → pneumaturia and faecaluria.

Sigmoid colon is most affected — highest intraluminal pressure.

• Diverticula = false (mucosa/submucosa) outpouchings, commonest in the sigmoid, from a low-fibre, high-pressure colon herniating at the vasa recta.
• Diverticulosis (present) vs diverticular disease (symptomatic) vs diverticulitis (inflamed = 'left-sided appendicitis').
• Complications: perforation/peritonitis, haemorrhage (lower GI bleed), fistula (colovesical → pneumaturia), stricture, abscess.
• CT is best in acute disease; colonoscopy after it settles (exclude cancer) — not during (perforation risk).
• Uncomplicated → antibiotics + high-fibre diet; abscess → drainage; perforation/peritonitis → Hartmann's procedure.