Flat colorectal neoplasms: definition, importance, and visualization on CT colonography.

OBJECTIVE: We discuss the definition of flat colorectal neoplasms, their clinical importance, CT colonography (CTC) findings, techniques for better visualization on CTC, and diagnostic pitfalls of such lesions.

CONCLUSION: Flat lesions appear on CTC as plaque-shaped mucosal elevations with or without a central depression, thickened haustral folds, and nodular mucosal surfaces. The sensitivity and optimal techniques of CTC for the detection of flat lesions have not yet been established. Three-dimensional endoluminal fly-through may be helpful for lesion detection. Fecal tagging helps in the distinction of true flat lesions from feces. I.v. contrast enhancement and the review with intermediate soft-tissue window settings, although not routinely used for CTC, may also help lesion visualization.