Computed tomography and magnetic resonance imaging of hepatic metastases.

Both computed tomography (CT) and MR imaging are useful in detecting and characterizing liver metastases. Currently, CT is more readily available and less expensive and thus tends to be more commonly used; MR imaging has a role in problem solving. The administration of intravenous contrast material is essential in almost all indications, with multiphasic imaging aiding in lesion characterization and detection. The use of multidetected CT (MDCT) optimizes vascular and multiplanar imaging but also has increases the complexity of the examination. Tissue-specific MR contrast agents can yield the highest rate of lesion detection and thus may be useful in presurgical planning. The liver is frequently involved with metastatic disease, with primary sites in the colon, breast, lung, pancreas and stomach.2 Although the dual blood supply to the liver may increase its vulnerability, studies have shown that the metastatic process is not random and cannot be explained on the basis of blood flow alone.26 The portal vein, which supplies 70% to 80% of the total blood flow to the liver,37 is believed to be the primary delivery system of metastatic gastrointestinal cancer to the liver.11 The endothelial lining of the hepatic endvasculature and sinusoids is unique in that fenestrations exist in the endothelial cells, but there is no underlying basal lamina.74 This configuration creates a potential communication between the intravascular and extracellular spaces and may predispose the liver to metastatic disease. Most clinically evident metastases receive their blood supply from the hepatic artery. Many metastases, however, including those which are hypovascular, and in particular those smaller than 1.5 cm, may receive substantial blood flow from the portal venous system.18, 24, 33, 34