CT colonography with intravenous contrast material: varied appearances of colorectal carcinoma.

Computed tomographic (CT) colonography is a noninvasive, rapidly evolving technique that has been shown in some studies to be comparable with conventional colonoscopy for the screening of colorectal cancer. Because colorectal cancer has a widely varying appearance at both endoscopy and CT colonography, familiarity with the gamut of morphologic appearances can help improve interpretation of the results. The addition of intravenous contrast material to CT colonography can aid differentiation of true colonic masses from pseudolesions such as residual stool and improves the depiction of enhancing masses that might otherwise be obscured by residual colonic fluid. In contrast to staging of most other tumors, staging of colorectal carcinoma depends more on the depth of tumor invasion than on the size of the primary mass. The diverse appearances of colorectal cancers at two- and three-dimensional CT colonography include sessile, annular, ulcerated, necrotic, mucinous, invasive, and noninvasive lesions. Imaging pitfalls that can simulate or obscure neoplasms are retained fecal material or fluid, incomplete distention, and advanced diverticulosis. (c) RSNA, 2005.