Diverticulitis

Digestive Inflamed colon pouches

Inflammation or infection of small pouches that bulge out from the wall of the large intestine.

Educational summary only — not medical advice, and no substitute for assessment by a clinician. Diagrams are simplified illustrations.

Small pouches push out through weak spots in the colon wall; trouble starts when one becomes blocked, inflamed and infected.

Overview

With age, small pouches called diverticula commonly bulge outward through weak spots in the wall of the large intestine — a harmless state called diverticulosis. Diverticulitis is when one of these pouches becomes inflamed or infected, causing pain and illness, usually in the lower-left abdomen.

How the system normally works

The colon is a muscular tube that moves and dries out waste. Its wall has natural weak points where small blood vessels pass through the muscle layer — exactly where pouches tend to form under pressure.

What goes wrong

Higher pressure inside the colon (linked to a low-fibre diet and constipation) pushes the lining out through these weak points, forming pouches. If a pouch becomes blocked or its thin wall is irritated, bacteria multiply and it inflames. This may stay mild and localised, or progress to a walled-off abscess, a perforation leaking into the abdomen, or scarring that narrows the bowel.

Cross-section diagram of the colon wall showing a diverticulum forming as the lining pushes through a weak point in the muscle. — Pouches (diverticula) form where pressure inside the colon pushes the lining out through weak points in the muscle wall.

Symptoms and why they happen

Lower-left belly pain, often steady and lasting days — the inflamed segment of colon.
Fever and feeling unwell — infection and inflammation.
Change in bowel habit — constipation or diarrhoea.
Bloating and nausea.
Sometimes blood in the stool (more typical of bleeding from a pouch than of infection).

Causes and risk factors

Older age
Low-fibre, high-red-meat diet
Obesity and physical inactivity
Smoking and some medications (e.g., NSAIDs)

How it's diagnosed

A CT scan of the abdomen confirms diverticulitis and grades its severity (simple inflammation vs abscess or perforation). Blood tests show infection. A colonoscopy is usually done after recovery (not during an acute attack) to inspect the bowel.

Diagram of diverticulitis complications: an abscess of pus beside the colon and a small perforation in the colon wall. — If inflammation worsens, a pouch can wall off into an abscess or perforate, leaking into the abdomen — the complications that need urgent care.

Treatment and management

Mild, uncomplicated cases are often managed at home with rest, fluids, and a temporary low-residue diet, sometimes antibiotics. More severe attacks need hospital care with intravenous antibiotics and bowel rest. An abscess may be drained through the skin; perforation or repeated severe attacks may require surgery to remove the affected segment.

Possible complications

Abscess, perforation with peritonitis, an abnormal connection to another organ (fistula), bowel narrowing (stricture), or significant bleeding.

Prevention and outlook

A high-fibre diet, good hydration, regular activity, and not smoking lower the risk of attacks. Most episodes settle with treatment, though some people have recurrences.

When to seek emergency care

High fever, severe or spreading belly pain, or a rigid abdomen — possible abscess or perforation.
Heavy rectal bleeding or inability to keep fluids down.