Imaging carries the diagnosis of diverticulitis, while colonoscopy is reserved for specific problems because of its risk during an acute attack.
Colonoscopy
Colonoscopy is contraindicated in patients who are suspected of having diverticulitis, because the chance of perforation is high in these patients. The indications for performing colonoscopy in patients suspected of diverticular disease are therefore limited to defining the source of lower gastrointestinal bleeding, treating diverticular bleeding, and excluding cancer.
When colonoscopy follows an episode of diverticulitis, it should be delayed until the acute inflammation has settled — 6–8 weeks, or until the acute symptoms have resolved, whichever is longer — so that the risk of perforation is lower and the mucosa can be inspected. It is brought forward only when warning features such as weight loss or a change in stool calibre raise the possibility of cancer.
Imaging
Ultrasound of the sigmoid colon by an experienced examiner and contrast-enhanced CT are both accurate, and either may come first in practice. Guidelines favour contrast-enhanced CT because it also grades severity and shows complications, while ultrasound has the advantage of avoiding radiation; when ultrasound is inconclusive or negative, CT follows. CT has a sensitivity of about 94–95% and a specificity of about 96–99% for the diagnosis of colonic diverticulitis. It uses water-soluble oral, rectal and intravenous contrast agents.
The main findings on abdominal CT with contrast in patients with diverticulitis are outpouching of the colonic wall — normally the outer wall of the colon is smooth, so outpouching indicates diverticulitis — thickening of the colonic wall, stranding of the peri-colic fat, peri-colic fluid accumulation, an abscess, and extravasated contrast agent.
A plain radiograph of the abdomen should be performed in any patient presenting with acute abdominal pain, to exclude perforation and obstruction.
Differential diagnosis
The differential diagnosis for diverticulitis is extensive:
- appendicitis — right-sided diverticulitis is most often misdiagnosed as appendicitis;
- inflammatory bowel disease (IBD);
- colorectal cancer;
- pelvic inflammatory disease;
- ovarian cyst rupture;
- ovarian torsion.