| Objective: The characteristic findings of pyogenic liver abscess(PLA) were studied through the correlation between three phase enhanced CT scan and MRI plain scan in order to offer the imaging basement for early diagnosis and treatment, so as to reduce the compilcation and mortality of this disease.Material and Method: The study were retrospectively reviewed twenty-one patients with PLA belonged to the early stage of abscess which were confirmed by puncture,blood culture, surgery and clinical treatment. Eighteen patients of them were underwent CT and MRI plain scan, and three phase enhanced CT scan. One patient of them were underwent CT and MRI plain scan, and three phase enhanced CT/MRI scan. Two patients of them were underwent MRI plain and three phase enhanced scan. Five patients of them had a single lesion. Sixteen patients of them had multiple lesions. Lesions of nineteen patients of them were compared in the same situation on CT and MRI to analysis the stage of lesions,sizes, morphology, the pattern of enhancement, the amount of cholangitis, portal vein thrombosis or stenosis, and pylephlebits. The multiple relationship between the area of pus cavity and perilesion edema in multiple and solitary fifty-five abscesses on MR imaging, and then the difference were compared between the former and the multiple relationship of the area of the necrotic part of the center and the perilesion solid part of 29 metastatic tumors. Six patients were selected according to lesions in the similar situation and their areas more than one segmental liver, and then averaged CT value were detected in plain scan and three phase enhanced CT scan to described the time-density curve in order to observe the hepatic hemodynamic alterations.Result: PLA was caused by infection originating in the biliary tract, portal circulation, arterial hematogenous spread, and directed extension. According to the process evolution of hepatic abscess, lesions were divided into two stages:the stage of infammation and the early stage of abscess. The two stages could be existent in the same period. In the group of this study, nineteen patients belonged to the former, eighteen patients belonged to the latter. (1) The stage of inflammation. Although causes were different, their imagings were either similar or different. Their similar imagings showed slight low attenuation or mildly hypointense on T1-weighted and mildly hyperintense on T2-weighted, which their area ranged from less than one segment to more than one liver lobe. In hepatic artery phase(PAH), transient hepatic attenuation difference (THAD) could be seen. It became iso-attenuation in portal venous phase(PVP), and then showed a more slight hyperattenuation than normal liver parenchyma in hepatic delay phase(PDH). There were several different aspects below the next content.①Infection originating in the biliary tract. Eight patients belonged to it. Cholangitis showed "ring sign" on T2-weighted in plain scan. It showed hyperattenuation "ring sign"in PAH and PVP, and then it became iso-attenuation in PLH. There was no difference (t= 1.43, p= 0.227) between the enhanced CT scan and MRI plain scan in the ability of showing the cholangitis.②Infection originating in the portal circulation. Seven patients belonged to it. It showed a widely lesion originating the result of pylephlebits. It showed "periportal halo sign" on T2-weighted imaging. It showed a low attenuation ring around portal on the enhanced CT scan. There was a significant difference (t= 3.23, p= 0.014) between the enhanced CT scan and MRI plain scan in the ability of showing the pylephlebits. The former was inferior to the later.③Infection originating in the arterial hematogenous spread. Two patients belonged to it. It showed some round and slight patched low attenuation or mildly hypointense on T1-weighted and mildly hyperintense on T2-weighted.④Infection originating in the directed extension. Two patients belonged to it. The area of lesion was limited. (2)The early stage of PLA. Thirteen patients' abscesses were multiple and five patients' abscesses were single. The perilesion edema and pus cavity (<2cm) were coexisting in the enhanced CT scan. It was so called "cluster sign". The "cluster sign" showed gradual enhancement and reduced attenuation in a less speed than normal liver parenchyma. The multiple relationship of areas between the perilesion edema and pus cavity of abscess and the area of the necrotic part of the center and the perilesion solid part of metastatic tumors had a significant difference(t=6.25, p<0.01). The former was more larger than the later. This multiple relationship between the perilesion edema and pus cavity of abscess was called "large edema area, small pus cavity ". (3) Transient hepatic attenuation difference (THAD):The ratio showing the sign in the obstruction area due to the result of pylephlebits or stenosis and thrombosis had a significant difference (x2=11.73, P=0.001) than the area of no obstruction. The ratio showing the sign in perilesion edema area had a more significant difference (x2=9.14, P=0.002)than normal liver parenchyma. (4)The comparison of density between the perilesion edema area and normal liver parenchyma:There was a difference (t=-2.99, P=0.005)between them in plain scan. The former was lower attenuation than the later. The time-density curve showed that the former had a significant enhancement than the later during PAH and then the density was similar during PVP. Moreover, the former which the speed of density reduced in a lower speed had difference (t= 3.93, P＜0.011)than the later during PLH.Conculsion: Making use full of their advantages of three phase enhanced CT scan and MR plain scan, the process evolution of early stage of pyogenic liver abscess could be disclosed in order to offer a new view for the early diagnosis and treatment of this disease.
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