Differentiation of Malignant Thrombus from Bland Thrombus of the Portal Vein in Patients with Hepatocellular Carcinoma: Application of Diffusion-weighted MR Imaging

Purpose: To investigate the utility of diffusion-weighted (DW) imaging in distinguishing bland thrombus from neoplastic thrombus in the portal vein in patients with hepatocellular carcinoma (HCC). Materials and Methods: In this retrospective institutional review board-approved HIPAA-complaint study, the imaging results in 25 patients (16 men [average age, 62.3 years; range, 35-75 years] and nine women [average age, 58.4 years; range, 32-69 years]; overall average age, 60.1 years; range, 32-75 years) with HCC and portal vein thrombosis who were examined with both contrast material-enhanced computed tomography (CT) and 1.5-T magnetic resonance (MR) imaging were reviewed. Axial echo-planar two-dimensional DW imaging was performed by using b values of 50, 400, and 800 sec/mm(2). A thrombus was considered neoplastic if it expanded the vessel or enhanced on the dynamic CT and MR images; otherwise it was considered bland. The signal intensity (SI) of the thrombus and HCC lesions in the same patients was compared on DW images. The results were evaluated by using the Fisher exact test. The apparent diffusion coefficients (ADCs) of HCC and thrombus were used to compute the ratio of the ADC of the thrombus to the ADC of the tumor. Results: On DW images, 15 of 19 neoplastic thrombi demonstrated same SI and four showed lower SI than the primary HCC. Each of the six bland thrombi had lower SI than the primary HCC (P<.001). The mean ADC of HCC and thrombus in the neoplastic thrombus group was 0.87 x 10(-3) mm(2)/sec and 0.88 x 10(-3) mm(2)/sec, respectively (P=.45). The ADC of the bland thrombus was 2.89 x 10(-3) mm(2)/sec, significantly higher than the ADC of the HCC (1.0 x 10(-3) mm(2)/sec, P<.0003). The ratio of the ADC of the thrombus to the ADC of the tumor in the bland thrombus group was 2.9 compared with 0.998 in the neoplastic group (P=.0003). Conclusion: DW imaging enables discrimination between bland and neoplastic portal vein thrombi when the ratio of the ADC of the thrombus to the ADC of HCC was lower than 2 and when the thrombi showed similar SI as the primary HCC when qualitative analysis was performed. (C) RSNA, 2010