Hypervascular liver lesions: differentiation of focal nodular hyperplasia from malignant tumors with dynamic gadolinium-enhanced MR imaging

The differentiating points between focal nodular hyperplasia (FNH) and malignant hypervascular liver lesions were studied at dynamic gadolinium-enhanced magnetic resonance (MR) imaging. Thirty-six patients with 50 hypervascular lesions (28 FNH, 12 hepatocellular carcinoma, nine metastases, and one cholangiocarcinoma) underwent unenhanced spin-echo (SE) T1- and T2-weighted imaging and T1-weighted gradient-recalled-echo imaging before and repeatedly for 10 minutes after intravenous bolus injection of gadopentetate dimeglumine. On unenhanced SE images, the signal intensity of 25 FNH lesions (89%) and 10 malignant tumors (45%) was homogeneous. A central scar was detected in 12 FNH lesions (43%) and in none of the malignant tumors. On dynamic gadolinium-enhanced images, all lesions had early vigorous enhancement that was homogeneous in 27 FNH lesions (96%) and in seven malignant tumors (32%) (P < .001). After administration of gadopentetate dimeglumine, central scars were seen in 22 FNH lesions (79%) and in one malignant tumor (4%) (P < .001). All FNH lesions (100%) and six malignant tumors (27%) had well-defined enhancement (P < .001). There was overlap in the enhancement pattern between hypervascular malignant lesions and FNH, but by using the combination of unenhanced and enhanced images, they could be distinguished.