Incidental Extracolonic Lesions: Computed Tomography

This chapter reviews the reported studies describing extracolonic findings on computed tomography (CT) in both CT colonography and minimal preparation CT (MPCT). It also discusses some of the issues raised by the detection of extracolonic findings at CT and of evaluating their contribution and presents the practical implications and handling of specific findings. Both CTC and MPCT are directed principally toward detecting colonic lesions, and, because of the cross-sectional nature of CT, other organs are also visualized. Detection of extracolonic lesions is thereby a by-product of the examination. Extracolonic lesions are frequently seen on CT colonography studies. These may be classified to be of low, moderate, or high significance. Findings of moderate importance are those that do not require immediate intervention but should be further evaluated for possible future intervention. Such intermediate lesions include gallstones, indeterminate renal lesions, adrenal lesions that are probably benign, uterine fibroids, and hiatal hernias. Lesions of major importance typically do require medical or surgical intervention, and these may include lymphadenopathy, aortic aneurysm, and solid masses in abdominal or pelvic viscera that may represent incidental malignancies. Extracolonic findings may be relevant to the staging of distant metastatic disease (TNM stage M disease). Sites of metastatic disease include the liver, lung, adrenal, peritoneum, ovaries, and bone. Liver metastases appear as low-density lesions on noncontrast CT; however, this appearance is not specific because benign lesions may be similar. Foci of fine calcification may be seen in mucinous adenocarcinomas. Liver metastases typically show irregular peripheral enhancement if intravenous contrast is given. The sensitivity of contrast-enhanced CT for the detection of liver metastases varies with lesion size but overall is ?60%.