Verification of multistep nature in development of hepatocellular carcinoma in the LEC rat using MR imaging method

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The purpose of this study is to elucidate the developing process of hepatic lesions in the Long Evans Cinnamon (LEC) rat by a longitudinal study of the same animals using MR imaging method. Prior to the longitudinal study we measured MR images of eleven aged LEC rats with pathologic correlation in order to characterize various hepatic lesions. As a result we can discriminate neoplastic/dysplastic nodules, peliosis hepatis, cholangiofibrosis and cyst by imaging. Then, we performed repeated imaging on the same twelve LEC rats at 60, 75, 90 and 100-weeks old.After the final measurement the animals were sacrificed and the hepatic lesions were histopathologically diagnosed after hematoxylin/eosin (H & E), and periodic-acid methenamine silver (PAM) staining. We have identified 4 neoplastic/dysplastic nodules, 24 peliosis hepatis, 7 cholangiofibrosis, 4 bile duct dilatation and 3 cystadenoma altogether in 12 rats. Among them 28 lesions were followed up at least two different time stages. Their imaging characteristics such as the T2 relaxation time and the image intensity ratio of lesion to liver parenchyma in T1-weighted images before and after Gd injection were well preserved in each lesion except for the prolonged T2 relaxation time observed in cystadenoma as it grows. The growth rate of lesions was also evaluated by following up the volume of each lesion in the longitudinal observation. Assuming an exponential growth we calculated the average doubling time of neoplastic/dysplastic nodule, peliosis hepatis, cholangiofibrosis, bile duct dilatation, and cystadenoma as 4.1, 5.8, 20.3, 8.7, and 4.6 weeks, respectively. This exact growth rate on individual lesions can only be obtained by a noninvasive imaging method like MR imaging.