Atypical Enhancement Pattern of Hepatocellular Carcinoma with Portal Vein Thrombosis on Multiphasic CT

Introduction: The 2005 American Association for Study of Liver Diseases (AASLD) diagnostic criteria allow non-invasive diagnosis of hepatocellular carcinoma (HCC) based on their enhancement pattern but we have observed a high incidence of atypical enhancement characteristics in HCC associated with portal vein thrombosis. This study seeks to examine the radiological features of this particular subgroup. Materials and Methods: Patients with HCC and portal vein thrombosis who underwent pre-treatment multiphasic CT imaging were drawn from a surgical database. The arterial, portal venous and delayed phase images were assessed qualitatively and quantitatively (with region of interest [ROI] analysis) for lesion hypervascularity and washout. The background enhancement of the left and right lobes of the liver was also quantified by ROI analysis. Results: Twenty-five lesions in 25 patients were selected for analysis. Qualitative analysis showed that 10/25 (40%) lesions demonstrated arterial hypervascularity while 16/25 (64%) lesions showed washout. Ten out of 25 (40%) lesions demonstrated both arterial hypervascularity and washout. Quantitative analysis showed that the average absolute lesion enhancement from precontrast to arterial phases was 49.1 (±17.1) HU for hypervascular lesions compared to 23.8 (±16.6) HU for non-hypervascular lesions (P <0.01). The mean absolute enhancement of the background liver parenchyma in the arterial phase was 13.79 (±7.9) HU for hypervascular lesions compared to 36.6 (±30.6) HU for non-hypervascular lesions (P = 0.03). Conclusion: A large proportion of HCC with portal vein thrombosis lack characteristic arterial hypervascularity, which may be secondary to compensatory increased arterial supply to the background liver. This is a potential pitfall when applying imaging criteria for diagnosis of HCC. Key words: HCC, Hypervascular, Pitfall, Wash-out