The #xrayoftheweek is this panel of MRI images, once again illustrating the use of diffusion weighted imaging in abdominopelvic MRI. These DWI, ADC and post-contrast T1-weighted images are from someone with a background of chronic liver disease. Which TWO major complications can you see?
a & d: diffusion weighted image (b=800)
b & e: ADC map
c & f: arterial phase post-contrast fat saturated T1
The TWO major complications of chronic liver disease illustrated here are:
(1) avid peripheral enhancement of a lesion in the right lobe with restriction of diffusion (images a, b & c) - highly suspicious for a hepatocellular carcinoma
(2) an expansile non-enhancing filling defect within the portal vein, with restriction of diffusion (images d, e & f) - highly suspicious for thrombus in the portal vein
Bland (i.e. blood clot) thrombus shows no enhancement at all on post-contrast imaging, where as tumour thrombus will show some enhancement depending on the original tumour. This early abstract described how tumour thrombus could be differentiated from bland thrombus using diffusion weighted imaging, with tumour typically having a lower ADC value than bland thrombus. However, a subsequent publication showed that there was considerable overlap in the ADC values of bland and malignant portal vein thrombus, and that signs on the conventional MRI sequences were the most useful to differentiate between the two entities ("distance from tumor to PVT of less than 2 cm, HCC size of greater than 5 cm, and arterial enhancement of PVT").
In this case, the signs on the conventional sequences pointed at this being a bland thrombus. The jury is still out on whether the ADC values can truly distinguish malignant from bland thrombus, but when reporting a liver MRI of suspected HCC, the portal vein should be examined carefully on both the conventional and diffusion weighted sequences, as both bland and tumour thrombus have characteristic signs on both types of sequences.
All the preceding DWI #xrayoftheweek posts can be found here.