Purpose: To test the clinical observation that the postcontrast attenuation level of focal nodular hyperplasia (FNH) at dual-phase computed tomography (CT) rarely exceeds 50% of aortic enhancement or absolute inferior vena cava (IVC) enhancement.
Materials and Methods: Nineteen pathologically proven FNHs in 17 female patients imaged with intravenous contrast-enhanced multidetector CT, of which 15 had arterial and venous phase acquisitions, were evaluated. Two radiologists retrospectively reviewed each CT study in consensus, using axial sections, multiplanar reconstructions, and 3-dimensional rendering techniques (volume rendering and maximum intensity projection). Recorded were precontrast and postcontrast attenuation of mass, the liver, the aorta, and the IVC; lesion size; segmental location; subjective appearance; contour; and presence of central scar, pseudocapsule, septations, feeding artery, or draining vein.
Results: The mean FNH attenuation level was lower than 50% of the mean aortic attenuation during the arterial phase (115 vs 144 Hounsfield units) and also lower than the mean IVC attenuation in the portal venous phase (142 vs 153 Hounsfield units). Across cases, the FNH arterial phase attenuation was lower than 50% of the aortic attenuation in 74% (14/19). The portal venous attenuation level of FNH was lower than or equal to that of the IVC in 80% (12/15). One of the 2 enhancement patterns was present in 100% (15/15) of cases.
Other common findings included feeding artery and draining vein (18/19), absence of pseudocapsule (18/19), and smooth contour (13/19). A central scar was identified in only 8 of 19 cases, and no lesion contained septations.
Conclusions: In this series of patients imaged with contrast-enhanced multidetector CT, most FNHs demonstrated arterial attenuation levels lower than 50% of the aorta and/or portal venous attenuation levels lower than or equal to those of the IVC.