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PI-RADS 2.1 Interpretation Pitfalls

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

Dr. P here, back with our 70 year-old man, PSA 7.3 in 2014, 8.8 in 2018, 8.9 in 2019. I think that's part of the reason the reader over-called this case as a PI-RADS 4, as opposed to a PI-RADS 3. But there are some other caveats here.

First, the diffusion. This particular diffusion image you're seeing has a b-value of 1600, so I'll put 1600 up here. But our ADC map should have been acquired, not with this, but with a b-value of 50, and then an intermediate b-value... I don't mind if you go anything from 600 to 900, somewhere in that range. And these are the two you use to make the ADC map. Now in this case, b-0 was used, b-1000 was used, and then b-1600. So I don't like the b-value lineup. So I would say this diffusion acquisition is analogous to Bad Santa, bad diffusion acquisition. Not the b-values that I would have chosen.

Now that, in part, could explain the discordancy between the diffusion image, which shows a bright area, and the ADC map, which barely shows an area of hypointensity. What's another cause of Bad Santa or bad diffusion? Patient has a hip prosthesis that distorts the magnetic field. That's a very common problem. It's even a bigger problem when they have hip prostheses on both sides. Another very common problem is failure of the technologist and the patient to prep properly and get air out of the rectum.

So these are very important pitfalls when deciding how to use the diffusion and ADC map, which, as you know in the peripheral zone, trump everything else. If the DWI is, say, a 4, score of 4, and the T2 score is a score of 2 or 3, the 4 is going to win out. The 4 is going to be the dominant thing that you use to come up with your final PI-RADS score. In the transitional zone, not so. In the transitional zone, the T2 morphology is going to be queen or king.

Now, one other caveat before we move off this particular vignette. This is an axial T2 with 2D. I'm going to pull down the 3D in the middle, and you can see this area, the PZ PM, and as we move out more laterally to the side, it's kind of ill-defined. I would describe it as a little bit mushy looking. There's a little bit of nodularity, but I think it's fair to say that it's heterogeneous and poorly defined. There's also some desiccation of a seminal vesicle, but it didn't enhance, it didn't diffusion restrict, it's not enlarged. In fact, it's shrinking a little bit right at the base. And this is not uncommon when you have a cicatrix, a scar, and then the ejaculatory duct in the vas deferens constrict. So this is a common scenario that can occur over a period of six months to a year. So don't let that mislead you into thinking you've got tumoral infiltration, unless you have diffusion restriction, mass effect and hypervascularity.

So in terms of scoring this, the T2 scoring, we would give this a T2 scoring of 3, heterogeneous signal intensity with non-circumscribed or somewhat rounded margins with moderate hypointensity. And I use the T2 2D for this assessment. The 3D, I use for mapping and volumetric analysis of the tumor itself.

Finally, another caveat. Contrast. Let's look at the contrast properties in the PZ PM near the midline. And there is some mild enhancement here. It didn't come in early. It came in modest to late, so that's a good sign. It's not very hypervascular in the early stages, and it's wedge-shaped. So wedge-shaped is often a sign of prostatitis, these ill-defined areas, and this is another caveat from PI-RADS 2.1. In the peripheral zone, mild or modest signal intensity on the T2 and mild diffusion restriction on either the DWI or the ADC map with an ill-defined, heterogeneous lesion in the peripheral zone, may be indistinct, linear, low bar, or diffuse, and these are frequently attributed to proven areas of prostatitis or granulomatosis prostatitis.

So on the contrast-enhanced study, no support for an aggressive tumor, more support for a wedge-shaped abnormality consistent with prostatitis. And indeed, this patient has a focal area of prostatitis, not aggressive cancer. Dr. P out.


Mastery Series: PI-RADS 2.1 Update

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Content reviewed: December 29, 2021

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