FDG and other radiopharmaceuticals in the evaluation of liver lesions

Liver nodules are common findings in medical practice, both in patients with and in those without chronic liver disease. These lesions have to be interpreted according to clinical history and biochemical findings. Conventional imaging (US, CT and MRI) is still the gold standard for evaluating liver nodules, while diagnostic flowcharts do not currently include PET/CT. Since the 1990s many studies have been conducted to assess a possible role for FDG PET or PET/CT in several liver pathologies. According to the literature, FDG PET (and later PET/CT) could be useful in detecting, staging and grading hepatocellular carcinoma, often leading to a change in therapy, and may even detect intrahepatic cholangiocarcinoma with adequate sensitivity. Moreover, FDG can allow more accurate staging of hepatic involvement deriving from other tumors (often underestimated by conventional imaging) and, therefore, more appropriate therapy in affected patients. Finally, FDG PET can also be used to evaluate 90Y microsphere therapy response. Other conditions (e.g., primary hepatic lymphoma when conventional imaging is inconclusive) may benefit from the use of FDG PET/CT, while benign lesions (e.g., focal nodular hyperplasia) show low FDG avidity. As regards non-FDG tracers, choline and acetate (ACE) have been evaluated in comparison with FDG and found to show good efficacy in detecting and staging well- or moderately differentiated HCC. However, their sensitivity in poorly differentiated HCC is very low, suggesting that dual-tracer investigation (FDG and choline/FDG and ACE) could be useful when non-invasive grading is required. Despite promising results, PET evaluation of liver nodules still seems to be far from routine application, mostly because of cost-related issues