The usefulness of diffusion-weighted imaging for differentiating portal vein thrombus from tumour embolus

To investigate the usefulness of diffusion-weighted imaging (DWI) for differentiating bland portal vein thrombus from tumour thrombus. Fifteen patients with clinical comprehensive diagnoses of portal vein thrombus were analysed retrospectively. The thrombus signal intensity on 21 DWI slices and apparent diffusion coefficient (ADC) values were analysed quantitatively. The portal vein thrombus was divided into four types (low/low, high/low, low/high, and high/high) based on the DWI/ADC ratios between the thrombus and liver parenchyma (rDWI and rADC, respectively). Twenty patients with portal vein tumour thrombi were used for comparison as controls. The average ADC value for the bland thrombus was 1.84 ± 0.70 × 10−3 mm2 s−1 (range: 0.46–2.77 × 10−3 mm2 s−1), and was 2.18 ± 0.51 × 10−3 mm2 s−1 (range: 1.39–2.82 × 10−3 mm2 s−1) for the liver parenchyma; the rADC was therefore 0.90 ± 0.45 (range: 0.26–1.86). The tumour thrombi were high/low and high/high type. The average ADC for the tumour thrombus was 1.25 ± 0.26 × 10−3 mm2 s−1 (range: 0.68–1.67 × 10−3 mm2 s−1), and 1.56 ± 0.33 × 10−3 mm2 s−1 (range: 1.11–2.34 × 10−3 mm2 s−1) for the liver parenchyma; the rADC was therefore 0.82 ± 0.16 (range: 0.39–1.08). There was no statistical difference in rADC values and rDWI/rADC classification performance between the bland and tumour thrombi. The ADC difference between portal vein bland and tumour thrombi was statistically significant, but the ADC values of bland thrombi have a wider range, which contains the ADC values of tumour thrombi with a narrower range. The elevated ADC values of the liver parenchyma adjacent to portal vein emboli may be helpful for the diagnosis of bland thrombi.