- Clinical suspicion of acute diverticulitis. For acute diagnostic work-up: ultrasound or CT proven diverticulitis. In the case of diverticulitis-negative ultrasound in clinically suspected patients an intravenous contrast-enhanced CT scan is mandatory for confirmation of diverticulitis or exclusion of other pathology. CT for Hinchey/Ambrosetti classification (which is a CT-based classification system) is needed for all patients, but can be delayed 1 day in those with ultrasound diagnosis. Staging diverticulitis is defined according the modified Hinchey/Ambrosetti staging, only stages 1a and 1b and "mild" diverticulitis (1a Confined pericolic inflammation, 1b Confined small (smaller than 5cm) pericolic abscess) are included;