Focal nodular hyperplasia and hepatocellular adenoma of the liver: Differentiation with multiphasic helical CT

OBJECTIVE. Differences of attenuation and enhancement patterns in focal nod ular hyperplasia and hepatocellular adenoma were evaluated and quantified u sing triphasic single-slice helical CT. MATERIALS AND METHODS. Forty-five histologically proven focal nodular hyper plasias in 27 patients and 18 hepatocellular adenomas in six patients were examined with helical CT. Quantitative evaluation included the following: a ttenuation of lesions, scar, and liver parenchyma during unenhanced, arteri al (20 sec after injection), and portal venous phases (70 sec after injecti on); relative enhancement of lesions and liver (the ratio between attenuati on in arterial phase and portal venous phase, respectively, and attenuation in unenhanced phase); and the prevalence of scar and its central vessel in focal nodular hyperplasia. RESULTS. The study showed no significant difference between mean attenuatio n values of focal nodular hyperplasia (mean +/- SD, 51.2 +/- 5.9 H) and hep atocellular adenoma (mean +/- SD, 56.3 +/- 7.8 H) in the unenhanced phase. In the arterial phase attenuation values were significantly higher in focal nodular hyperplasia (mean +/- SD, 117.9 +/- 15.1 H) than in hepatocellular adenoma (mean +/- SD, 80.1 +/- 10.5 H): In the portal venous phase no sign ificant differences in attenuation values were detected between focal nodul ar hyperplasia (mean +/- SD, 112.1 +/- 20.4 H) and hepatocellular adenoma ( mean +/- SD, 110.2 +/- 12.9 H). For enhancement parameter thresholds separa ting focal nodular hyperplasia from hepatocellular adenoma, the following w ere found: the relative enhancement was higher in 100% of the focal nodular hyperplasias and lower than or equal to 1.6 (accuracy, 96%) in 87% of the hepatocellular adenomas. CONCLUSION. Triphasic helical CT combined with quantitative evaluation of l iver lesions offers the possibility of detecting differences in liver lesio ns that are visually similar on CT. The attenuation and relative enhancemen t in the arterial phase show significant differences that make accurate dif ferentiation between focal nodular hyperplasia and hepatocellular adenoma p ossible.