Lesion identification taps new strategies

The largest solid organ in the human body and the largest gland, the liver dominates the field of abdominal radiology. Its complex arrangements for blood supply-drawing on not one but two separate sources-only add to the challenge.

Radiologists' interest in the liver is also driven by the vast array of problems that it can host. Pick any pathology, and you are likely to find that the liver is somehow involved. This is perhaps not surprising, given that the organ has an estimated 500 separate functions.

"The liver is a frequent site of primary tumors, metastatic tumors, infection, and trauma," said Dr. Erik Paulson, chief of abdominal imaging at Duke University Medical Center in North Carolina. "This makes it an important organ to evaluate, completely and compulsively, in an abdominal imaging exam."

Primary liver cancer is the sixth most commonly diagnosed cancer and the third most common cause of death from cancer worldwide. Rates in Europe and the U.S. have traditionally been far lower than those in eastern Asia and Africa, but the number of cases is growing. This increase, primarily in hepatocellular carcinoma, has been caused by mounting infection rates of hepatitis B and C. Instances of chronic diffuse liver disease in the developed world, linked to alcoholism and obesity, are growing as well.

The liver is also the most common site of metastases from gastrointestinal tumors, including pancreatic, gastric, small bowel, and colorectal cancers. Metastases from breast cancer and lung cancer can be found in the liver as well, as can a variety of benign lesions: cysts, hemangiomas, adenomas, and focal nodular hyperplasia. Just finding all these lesions is one thing. Identifying them accurately so patients can be managed appropriately is another matter altogether.

Given the variety of possible pathologies, a "one size fits all" diagnostic workup is clearly out of the question. Imaging protocols in the liver must be tailored to the specific problem. These protocols will be reasonably similar from institution to institution, though certain geographic trends can be observed.

Liver imaging protocols at Duke are typical of those employed at most U.S. hospitals, according to Paulson. CT is the workhorse for liver and abdominal imaging, with MRI reserved for problem solving. Liver lesions are most likely to be identified during a CT exam and then characterized on contrast-enhanced MRI. Ultrasound is used to evaluate the biliary tract and to screen patients with chronic liver disease, such as cirrhosis, for any signs of HCC.