The development of high-speed helical computed tomography (CT) and organ-specific scanning protocols has markedly improved preoperative CT staging of liver tumors. Three-dimensional reconstruction and arterial and venous imaging without invasive arterial angiography can be accomplished with currently available equipment and software programs. For hepatocellular carcinoma (HCC), the helical CT detection rate for small tumors (40% to 60%) is less than that for hepatic metastases, owing to the difficulty of detecting small tumors in cirrhotic livers and particularly of distinguishing HCC from macroregenerative nodules. Further improvements in morphologic CT imaging over the next 5 years will include rapid data acquisition during a single breath-hold, rapid scan sections with thinner individual sections, multidetector systems, and multiplanar 3-dimensional reconstructions and volume rendering with even more detailed image resolution.
Magnetic resonance (MR) imaging is more sensitive than helical CT in the detection of early HCC and in distinguishing between HCC and macro-regenerative nodules. The development of liver-specific MR imaging contrast agents has further improved the diagnostic accuracy in both primary and metastatic liver malignancies, and such agents can also help establish the probability of a benign versus a malignant liver tumor.
Paralleling the improvements in CT and MR imaging, ultrasonography equipment and image detail have continued to improve. Transcutaneous ultrasonography has been used to detect liver tumors, to guide percutaneous biopsies of liver tumors, and to guide therapy for selected tumors with direct injection or ablation techniques. Ultrasonography is rarely used as a screening or follow-up evaluation tool in patients with metastat-ic liver tumors, but because it is a readily available and relatively inexpensive technology, ultrasonography is commonly used in programs that screen high-risk populations for the development of HCC. In studies from the United States and Europe, ultrasonography has been shown to be superior to serum alpha fetoprotein measurement for the detection of early HCC in patients with chronic viral hepatitis.
The most important use of ultrasonography in hepatobiliary surgery is intraoperative ultrasonography, which is particularly helpful in cirrhotic patients with HCC. Intraoperative ultrasonography has become the gold standard against which all other diagnostic imaging modalities are compared for detecting the number and extent of tumors and the association of tumors with intrahepatic blood vessels in both primary and metastatic liver tumors.
Rapid progress in the 1990s in laparoscopic surgery included the development of laparoscopic ultrasound probes. Laparoscopy provides the advantage of a visual inspection to exclude the presence of extrahepatic disease on the peritoneal surfaces in the abdominal cavity, and laparo-scopic ultrasonography can be performed on the liver and spleen and, in selected instances, on retroperitoneal structures such as the kidneys, adrenal glands, and pancreas. Laparoscopic evaluation and laparoscopic ultrasonography have further reduced the rate of unnecessary exploratory laparotomy and thus increased the proportion of patients who undergo successful hepatic resection at the time of laparotomy. Like intraoperative ultrasonography, laparoscopic ultrasonography reveals small primary or metastatic liver tumors not visualized on preoperative CT or MR imaging studies in up to 15% of patients.
Positron emission tomography (PET) is a nuclear medicine study that is being widely evaluated in patients with malignant disease. PET does not provide the anatomic detail and definition of modern CT or MR imaging, but it does offer the potential advantages of whole-body imaging and the ability to detect subclinical disease in the liver and at extrahepatic sites. PET has been less useful in the evaluation of HCC, as many of these tumors do not have a significantly higher uptake of the radioisotope compared with the surrounding hepatic parenchyma. Novel radioisotopes and combinations of these radioactive compounds are being studied to further improve imaging sensitivity and specificity in patients with HCC and hepatic metastases.
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