CT for the evaluation of carcinomas in the colon and rectum.

The role of conventional CT in assessing patients with colorectal tumors is well established. The low accuracy of CT for identifying early stages of primary colorectal cancers prevents the routine use of CT for preoperative staging. Nevertheless, CT is useful in examining patients suspected of having extensive disease, in deciding whether a patient will benefit from preoperative radiation, in designing radiation ports, and in detecting complications related to the neoplasm. For recurrent colorectal neoplasm, CT has the premier role. CT surpasses colonoscopy in detecting early masslike tumor recurrence at the anastomotic site because of its extrinsic component, and CT and MRI are the only methods that can fully evaluate cases of total abdominoperineal resection. After total abdominoperineal resection, however, CT cannot determine with certainty that a soft tissue density in the surgical bed represents recurrent tumor. In patients with colorectal neoplasms, preliminary results with multiplanar and three-dimensional reconstructions of helical CT images are promising, but their role needs further investigation.