Usefulness of conventional MRI sequences and diffusion-weighted imaging in differentiating malignant from benign portal vein thrombus in cirrhotic patients.

OBJECTIVE: The objective of our study was to determine the value of diffusion-weighted imaging (DWI) and conventional MRI (non-DWI sequences) in differentiating benign portal vein thrombus (PVT) from malignant PVT in cirrhotic patients.
MATERIALS AND METHODS: A retrospective search of the department of radiology's MRI database of examinations performed from October 2006 through December 2010 for "portal vein thrombosis" and "cirrhosis" and "hepatocellular cancer" was performed. Patients who underwent diagnostic DWI and had thrombus shown to be rapidly (< 3 months) increasing in size despite anticoagulation therapy were considered to have malignant PVT (n = 16 cases) and patients with MRI findings showing stability or reduction in the extent of thrombus over a 12-month follow-up were considered to have benign PVT (n = 20 cases). Two blinded and independent reviewers analyzed the DW images and conventional MR images.
RESULTS: There was no difference in the distribution of patients by age (p = 0.25) or sex (p = 0.68) between the benign and malignant PVT groups. On multivariate analysis, the only parameter to predict the type of PVT was the size of HCC (p = 0.05); other parameters were excluded from the model. There was substantial overlap in apparent diffusion coefficient (ADC) values and PVT/liver ADC ratios of benign PVT and malignant PVT. The presence of at least two of the three following MRI findings had a sensitivity of 100% and specificity of 90% for the diagnosis of malignant PVT: distance from tumor to PVT of less than 2 cm, HCC size of greater than 5 cm, and arterial enhancement of PVT.
CONCLUSION: Signal-intensity characteristics on DWI and measured ADC values do not reliably differentiate benign PVT from malignant PVT. On the other hand, careful assessment of conventional MRI findings may allow this distinction, thus obviating biopsy.