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MRI Online

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PI-RADS 2.1 Pitfalls

4 min.
Pomeranz, Stephen
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
CME Eligible
Includes DICOM files

Dr P. here talking about potential pitfalls in PI-RADS 2.0 and 2.1 in this case of a 70-year-old man who's had a rising PSA, about 7.3 in 2014, 8.8 in 2018, and 8.9 in 2019. This is his two-year followup. He had an equivocal scan that didn't have an abnormality in the same locus as we see today in 2017. Nevertheless, he had a biopsy. The biopsy showed some low-percentage areas of Gleason 6, and now we have this study from 2019.

On the far left, we have the B 1600 image and the ADC map. You can see that the lesion in the PZpm, which is a new mapping designation, close to the midline peripheral zone posteromedial has some diffusion restriction, yet it barely shows up on the ADC map. So these are discordant, and this generally brings you into a DWI score, not a PI-RADS score, but a DWI score of 3. In other words, a focal discrete area different from the background. It's hypointense on the ADC map but not so much so. It's mildly hypointense and/or focally hyperintense on the high b-value DWI, but not both. In other words, it's not intensely bright here and intensely dark here. For it was, it wouldn't get a score of 3. It'd get a score of 4, or if it's really large, a score 5.

So the DWI score is 3, kind of in the intermediate zone. Now, I think the interpreter, who called the entire study a PI-RADS 4, probably overread it. They probably overread it because this area of diffusion restriction wasn't present before, the PSA is rising, and we have an equivocal kind of tweener intermediate situation. But which way should this interpreter have gone? Probably should've gone to a PI-RADS 3, and the reasons are as follows: The DWI score is a 3, for reasons we already mentioned.

What about the T2 appearance? Well, this would be a a T2 score in the peripheral zone of 3. What's a 1? A 1 is uniform hyperintense signal. What's a 2? Linear or wedge-shape hyperintensities or diffuse hyperintensity throughout. Yeah, that's pretty diffuse, but not all the way around, not throughout. So I would qualify this one as heterogeneous signal intensity, non-circumscribed, kind of ill-defined, some areas rounded. The degree of hypointensity is moderate. So I would give this T2 score a 3. What would be a T2 score of 4? Circumscribed, homogeneous, moderate hypointense focal mass surrounded by a high signal about it, confined to the prostate, but under 1.5 cm.

So you see the T2 score's a 3, the DWI score is a 3, and unless there was something really profound on the contrast-enhanced MRI, which there wasn't, you should go with a PI-RADS 3 for this case. This patient did undergo a biopsy and the biopsy was entirely normal throughout the prostate, except for one locus of a Gleason 6 in which 10% of the chip was affected with a Gleason 6-something that you probably wouldn't have seen on an MRI. So that's an incidental finding. So, essentially, this is a negative biopsy outcome, and the patient has a PI-RADS 3, not a PI-RADS 4. It was overread for reasons mentioned.

There are a few other caveats I want to share with you in this case of pitfalls. It is riddled with pitfalls, and we'll see those in the next vignette. Dr. P. out.


Mastery Series: PI-RADS 2.1 Update

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Content reviewed: December 29, 2021

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