Importance of small (< or = 20-mm) enhancing lesions seen only during the hepatic arterial phase at MR imaging of the cirrhotic liver: evaluation and comparison with whole explanted liver.

PURPOSE: To retrospectively assess the importance and imaging appearance of small (< or = 20 mm in diameter) hepatic arterial phase-enhancing (HAPE) lesions that are occult during portal and/or equilibrium phases and at unenhanced T1- and T2-weighted magnetic resonance (MR) imaging and to determine the gross pathologic diagnosis with whole-liver explant comparison.

MATERIALS AND METHODS: This retrospective study was approved by the institutional review board and compliant with HIPPA. Forty-six patients with cirrhosis who underwent MR imaging and transplantation within 90 days were evaluated with breath-hold T2-weighted and volumetric three-dimensional gadolinium-enhanced gradient-echo MR imaging in the hepatic arterial, portal venous, and equilibrium phases at 1.5 T. Three readers, who were blinded to the pathologic results, retrospectively reviewed the MR images in consensus for small HAPE nodules that were occult at T2-weighted and portal and/or equilibrium phase MR imaging. Only patients with nodules that enhanced during the arterial phase were included in the final study group, which included 16 patients (12 men and four women) aged 18-66 years (median age, 51.5 years). Explanted livers were serially sliced into 5-8-mm-thick sections to evaluate dysplastic nodules and hepatocellular carcinomas (HCCs). The Fisher exact test was performed to determine whether there was a relationship between HCC and the presence of a neoplastic HAPE-only lesion. The Mann-Whitney test was used to determine if patients with at least one neoplastic HAPE-only lesion had a larger number of non-HAPE-only lesions.

RESULTS: The 16 patients had 45 HAPE-only lesions; three (7%) of which were neoplastic, including one overt HCC, one HCC arising in a dysplastic nodule, and one dysplastic nodule. None of the remaining 42 HAPE-only lesions (93%) had correlative pathologic findings. All three neoplastic lesions seen only during the arterial phase were found in eight patients with concomitant HCC, who also had an additional 13 pathologically proved nonneoplastic HAPE-only lesions. In eight patients without HCC, none of the HAPE-only lesions were neoplastic. A concomitant non-HAPE-only neoplastic lesion was not a significant (P = .2) predictor for the presence of at least one neoplastic HAPE-only lesion. There was a preliminary but insignificant (P = .13) indication that the number of non-HAPE-only lesions tends to be higher in patients with neoplastic HAPE-only lesions.

CONCLUSION: The majority (93%) of HAPE-only lesions that are occult at T2-weighted and portal and/or equilibrium phase MR imaging are nonneoplastic, even in patients with pathologically proved HCC.