RADIOLOGY: GASTROINTESTINAL: GI: Case# 93: COLON CA. 69 year old male with abdominal pain. A circumferential mass lesion is seen in the transverse colon. There are multiple, diffuse low attenuation lesions within the liver. Multiple sites of adenopathy are seen, particularly in the periportal and peripancreatic regions. Adenocarcinoma of the colon appears as an irregularly marginated, roughly spherical soft tissue mass, as seen in the transverse colon above. Larger tumors may demonstrate central low attenuation representing necrosis. Lesions of the rectum and rectosigmoid are seen as asymmetric or circumferential thickening of the bowel wall with deformation and narrowing of the lumen. Other findings include: extension of the tumor intopericolonic fat, invasion of adjacent structures, lymphadenopathy, adrenal or liver metastases, hydronephrosis, ascites, and masses in the abdominal wall, omentum or mesentery. Common sites of local extension from the rectosigmoid (as seen by marginal obscuration) include pelvic muscles, bladder, prostate, seminal vesicles, and ovaries. Hepatic metastases vary in their CT apperance. Borders may be sharp, ill-defined, or nodular with round, ovoid, or irregular shape. Attenuation is usually lower than that of the surrounding liver both before and after contrast administration (although mets may become iso- or hyperdense after contrast). Metastases may become necrotic with low attenuation centers and/or display calcifications.