Natural course of hypovascular nodules detected on gadoxetic acid-enhanced MR imaging: Presence of fat is a risk factor for hypervascularization

Purpose: Hypovascular nodules that exhibit hypointensity in hepatocyte-phase images of gadoxetic acid-enhanced magnetic resonance (MR) imaging are frequently encountered in clinical practice. We investigated risk factors for the development of these nodules into hypervascular hepatocellular carcinoma (HCC). Methods: We retrospectively reviewed our institutional database and identified 302 patients who underwent gadoxetic acid-enhanced MR imaging for suspected or confirmed HCC from February 1, 2008 to January 30, 2011. We excluded patients who were examined for metastasis of other malignancies or for other hepatic tumors, such as focal nodular hyperplasia. We identified hypovascular nodules that were hypointense in hepatocyte-phase images, recorded their characteristics, and calculated the cumulative hypervascularization rate for nodules that were followed up. Results: Of the 302 patients, 82 had hypovascular nodules (178 nodules; mean size, 9.3 mm). Sixty nodules were followed up for over 6 months, and eight progressed to hypervascular HCC. Hypervascularization occurred more frequently in nodules with fat than those without (P<0.01). The cumulative hypervascularization rate was 5.1% over a year. Conclusion: The presence of intralesional fat was found to be a risk factor for hypervascularization of hypovascular nodules that exhibited hypointensity in the hepatocyte-phase images of gadoxetic acid-enhanced MR imaging.