AKT · Gastroenterology/Colon & rectum

Diverticular disease & diverticulitis

Acquired colonic mucosal outpouchings (low-fibre, raised intraluminal pressure) ± inflammation

Overview

Diverticula are acquired outpouchings of colonic mucosa (commonest in the sigmoid), driven by low fibre and raised intraluminal pressure. Diverticulosis (asymptomatic) → diverticular disease (symptomatic — pain, altered habit) → diverticulitis (inflamed/infected diverticulum: left iliac fossa pain, fever, raised inflammatory markers). Complications: perforation/abscess, fistula, obstruction, bleeding. Uncomplicated diverticulitis may need no antibiotics.

Recognise

Diverticulosis: incidental, asymptomatic; Diverticular disease: intermittent left lower abdominal pain, bloating, altered bowel habit
Acute diverticulitis: constant LEFT iliac fossa pain, fever, tenderness, raised CRP/WCC, altered bowel habit ('left-sided appendicitis')
Complications: perforation (peritonitis/abscess — Hinchey), colovesical fistula (pneumaturia/faecaluria), stricture/obstruction, painless brisk PR bleeding

Red flags

Complicated diverticulitis (peritonitis, abscess, perforation, obstruction, fistula) → same-day surgical assessment + CT
Uncontrolled pain / systemic sepsis / unable to tolerate oral antibiotics → admit

Differentials & how to tell them apart

Colorectal cancerweight loss, anaemia, mass, change in habit — colonoscopy after settling to exclude

Appendicitisright iliac fossa (but a long appendix/redundant sigmoid can mimic)

Ischaemic colitis / IBDbloody diarrhoea, vascular/inflammatory pattern

Gynaecological causesovarian/PID in women — examine/pregnancy test

Investigations

Acute: CRP/WCC, CT abdomen/pelvis (the key test — confirms diverticulitis, grades complications). Colonoscopy AFTER the acute episode settles (exclude cancer) — avoided acutely (perforation risk).

Management

Analgesia (avoid NSAIDs/opioids) ± co-amoxiclav; CT + surgery if complicated

1Uncomplicated acute diverticulitis: analgesia (paracetamol — AVOID NSAIDs/opioids), and oral co-amoxiclav for 5 days if systemically unwell (a no-antibiotic strategy is reasonable if systemically well). Safety-net.Gate: Complicated disease (peritonitis, abscess, perforation, obstruction, fistula on CT) → same-day surgical assessment + IV antibiotics ± drainage/surgery; colonoscopy is done AFTER recovery (not acutely) to exclude cancer
2Abscess → radiological drainage; perforation/peritonitis → resection (Hartmann's); recurrent/complicated → elective resection; interval colonoscopy.

Simple analgesia (paracetamol) — AVOID NSAIDs/opioids — NSAIDs and opioids increase perforation risk

Oral co-amoxiclav (5 days) if systemically unwell — uncomplicated diverticulitis; consider NO antibiotics if systemically well

IV antibiotics + surgery — complicated disease (abscess → drainage; perforation → resection/Hartmann's)

Key points

Left iliac fossa pain + fever + raised inflammatory markers = acute diverticulitis ('left-sided appendicitis') → CT; antibiotics only if unwell, avoid NSAIDs/opioids. Pneumaturia = colovesical fistula. Always colonoscope after recovery to exclude cancer.

Monitor & prognosis

Resolution; interval colonoscopy; recurrence.

Most settle; complications need surgery.

Source: NICE NG147; CKS Diverticular disease