The study should be performed after intravenous and oral water-soluble contrast. If oral contrast is not tolerated or if oral contrast does not reach the colon because of ileus, a gentle water-soluble contrast enema, which is safe, may be used. On CT, diverticula are seen as 5 to 10 mm collections of gas or contrast protruding from the wall of the colon. Symmetrical thickening of the colonic wall may be noted. Perforation and fistula may be visualized by means of air or contrast.
Abscess is seen as one or more discrete fluid collections.
If the abscess communicates with the colonic lumen, contrast may enter the abscess cavity. When abscess is detected, the feasibility of CT-guided drainage can be determined. Pelvic and abdominal ultrasonography is particularly useful in women when gynecologic disorders are part of the differential diagnosis. Diverticula are echogenic and produce acoustic shadowing. With graded compression sonography, the colonic wall in diverticulitis is thickened, noncompressible, and hypoechoic.