Characterization And Differential Diagnosis Of Atypical Fatty Liver: CT And MRI

[Objective] To demonstrate the CT and MRI appearances of atypical fatty liver, analyse its characterization and differential diagnosis, choose the optimal modalities of CT and MRI, discuss the pathogenesis of atypical fatty liver, and introduce a new radiological classification of fatty liver.[Materials and Methods] There were 37 cases of atypical fatty liver and 26 cases of atypical intrahepatic space-occupying lesions enrolled in this study. Thirty-seven cases of atypical fatty liver which performed precontrast CT scan were arbitrarily divided into three groups. Among them, sixteen cases were focal spared region. 9 focal fatty infiltration and 12 heterogeneous fatty infiltration. Of the 37 cases, twenty-eight underwent dynamic contrast enhanced CT examination, twenty-four cases were performed MRI, including chemical shift in- and out-phase imaging using gradient echo (GRE) sequence, based on these two pulse sequences, the diagnosis of fatty liver were comfirmed. In addition, enhanced MRI were performed after intravenous administration of Gd-DTPA in two cases and superparamagnetic iron oxide (SPIO) in 5 cases. Meanwhile, among the 26 cases of atypical intrahepatic space-occupying lesions, hemangiomas were found in eight cases, hepatocellular carcinomas (HCC) in 15, including 2 cases of small HCC, and each one in cholangiocarcinoma, metastasis and focal nodular hyperplasia (FNH).[Results ] Among the precontrast CT and tri-phases conrast enhanced scans, the fat-infiltrated regions had lower density than that of normal liver parenchyma in all of the 37 cases, and mean density discrepancy between lesion and normal liver parenchyma had no significant difference (/J>0.05)in all the three groups ofatypical fatty liver. In addition, among the 34 lesions of 24 cases who were performed plain MRI scan (focal spared region was referred to lesion in this group), twenty-two lesions showed isointense on both TiWI and T2WI. On out-phase image, the fat-infiltrated regions of 24 cases all had visible significantly decreased signal intensity, compared with the normal liver parenchyma, no lesions were found on Gd-DTPA enhanced image of two cases of atypical fatty liver because they showed isointense on TiWI,. In the 5 cases of SPIO-enhanced examination, the signal intensity discrepancy between lesions and normal liver parenchyma on T^WI was similar to that of precontrast MRI scan. Most of the atypical intrahepatic space-occupying lesions showed characterized appearances on dynamic contrast enhanced CT and precontrast MRI examination. Several atypical lesions such as HCC and small hemangioma could not be made a correct diagnosis until Gd-DTPA and SPIO enhancement were performed.[ Conclusion J As to the characterization and differential diagnosis of atypical fatty liver, several critical signs may be valuable : (fjEach kind of atypical fatty liver has its typical common sites, almost all of them were ill-defined; (2) On precontrast and tri-phases postcontrast CT scan, the fat-infiltrated region has a lower attenuation than that of normal liver parenchyma, and the attenuation discrepancy between the fat-infiltrated region and normal liver parenchyma hasn't significant difference consistently; (3)Most of lesions showed isointense on both TjWI and T;WI, so it's difficult to identify them, the rest of lesions usually has ill-defined margin; On out-phase image, all the abnormal regions have significantly decreased signal intensity; 'XGd-DTPA and SPIO enhanced MRI play an important role on differential diagnosis of atypical fatty liver. Based on the CT, MRI characterization that mentioned above, we introduce a set of optimal modalities procedure to the fatty liver which has atypical appearance on plain CT scan. The third inflow to liver play an important role on the pathogenesis of atypical fatty liver, as a part of third inflow, the cystic vein system, parabiliary vein system and epigastric-paraumbilical vein system have a close relation to the formation of focal spared region and focal fatty infiltration in segment I and...