First and second year — the floor first, then every step
Find the inflamed diverticulum, then decide complicated or not — abscess (and its size), extraluminal gas far from the colon, fistula, obstruction — because that decides antibiotics, drainage or surgery.
Orient first
Diverticulitis is inflammation around a diverticulum; the diverticulum itself is often the centre of the fat stranding, with bowel wall thickening on either side.
Sigmoid in the West; right-sided (caecal/ascending) diverticulitis is common in Asian populations and mimics appendicitis.
Colon cancer can mimic it: a long segment with shouldered margins, pericolic nodes and no diverticula suggests tumour — follow-up colonoscopy is part of the report.
Acquire the study
Portal venous phase CT; lung or wide window for extraluminal gas.
The manoeuvre
Locate the inflamed segment: wall thickening, pericolic fat stranding centred on a diverticulum.
Wide window: extraluminal gas — adjacent bubbles versus distant free gas.
Abscess: a rim-enhancing collection; measure it (a size around 3–4 cm often prompts drainage — verify local practice).
Fistula: gas in the bladder or vagina, colovesical tract.
Obstruction, portal venous gas (pylephlebitis), and the length and margins of the segment (tumour features).
What confirms it
Segmental colonic wall thickening with pericolic inflammation centred on a diverticulum.
What licenses you to exclude it
A normal CT excludes diverticulitis as the cause; report the alternative diagnosis.
The classic misread
Calling a perforated colon cancer diverticulitis — look at the segment length and the margins.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Diagnostic criteria
Diverticulitis · Hinchey classification — how to report it
a named surgical classification: Ia confined pericolic inflammation/phlegmon, Ib pericolic abscess, II distant abscess, III purulent peritonitis, IV faecal peritonitis
CT can stage abscess and free perforation; it cannot always separate Hinchey III from IV. Modified Hinchey and WSES systems exist — name which one the local team uses. Versioned criterion — verify against the current edition before clinical use.
CT
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.