To analyze the morphologic and enhancement patterns of focal nodular hyperplasia (FNH) of the liver observed at triphasic helical CT.

The triphasic helical CT findings of 15 pathologically-proven FNHs in 15 patients (male: female = 7:8; mean age, 40 years) were retrospectively analyzed. Triphasic helical CT images were obtained at 30 secs (arterial phase), 70 secs (portal phase), and 3 mins (equilibrium phase) after the initiation of contrast injection of a total of 120 mL nonionic contrast material at a rate of 3 mL/sec. Image analysis focused on the morphologic and enhancement patterns of the FNHs. Morphologically, their size and margin conspicuity were determined, as well as the presence or absence of a capsule, central scar, malformed arterial vessel, calcification, and mosaic pattern. As for the enhancement pattern, the degree of tumor enhancement (hyper-, iso-, or hypoattenuation) was compared with the surrounding hepatic parenchyma at each phase. All hyperattenuating FNHs were further analyzed after dividing them into two groups, strongly and weakly enhanced.

Ten of the 15 tumors were less than 3 cm in diameter. With regard to the other morphologic parameters, a central scar, malformed arterial vessel, and capsule were found in four, four, and five FNHs, respectively. Eleven FNHs showed hyperattenuation, with strong enhancement at the arterial phase. During the portal and equilibrium phases, the enhancement pattern changed to iso- or hypoattenuation in nine and 13 FNHs, respectively. Of six hyperattenuating FNHs at the portal phase, five were weakly enhanced.

Though our sample was small, we found that FNHs were hyperattenuating lesions, strongly enhanced at the arterial phase but iso- or hypoattenuating during the portal and equilibrium phases. A central scar, malformed arterial vessel, and capsule were observed fairly frequently. Thus, for the differentiation of FNH from other hypervascular hepatic tumors, precise recognition of their CT findings is important.