if you’ve been diagnosed with prostate cancer (PCa) you are probably familiar with the Gleason grade, a numeric value from 1-5 that indicates aggression. It is derived by microscopically examining and evaluating the appearance of cells in biopsy tissue samples (physical evidence judged by a pathologist). However, you may not be familiar with a different numeric system called the Prostate Imaging Reporting and Data System (PI-RADS). The Gleason system was designed by and for urologists, while PI-RADS was designed by and for interventional radiologists. Why two systems?

The answer lies in the increasing sophistication and accuracy of noninvasive multiparametric MRI (mpMRI). mpMRI does not replace the cellular information that is the foundation for the Gleason grade, but it can do things that pathology cannot. Today, mpMRI is almost universally recognized by both urology and radiology as 1) a precursor to biopsy, 2) a guidance and confirmation system for focal ablation of prostate tumors, and 3) a way to monitor treatment results during follow-up.

Both Gleason grade and PI-RADS use a 5-point scale. As I wrote in an earlier blog, “The Gleason scale ranges from 1 to 5, where 1 indicates no cancer at all, and 5 indicates very aggressive disease. In that sense, PI-RADS is similar, but it’s an interpretation of images, not actual cells. Thus, it has to do with interpreting the likelihood of cancer depending on what the images show.” PI-RADS is reported as:

Level I	Most probably benign (not cancer)
Level II	Probably benign
Level III	Indeterminate (not definite if it’s benign or cancer)
Level IV	Probably cancer
Level V	Most probably cancer

Evolution of mpMRI

Prostate MRI began with two imaging sequences, T1-W and T2-W, that revealed anatomy. It was useful for staging patients but less able to discriminate nonaggressive tumors (insignificant PCa) from aggressive ones (significant PCa). Gradually, other sequencing “parameters” were developed that could define tissue characteristics and distinguish tumor aggression levels: Diffusion Weighted Imaging (DWI), Dynamic Contrast Enhanced imaging (DCE), and spectroscopy (MR-S). These parameters opened up new diagnostic possibilities, guiding such decisions as whether a needle biopsy is warranted, and if so, where to place biopsy needles (MRI-guided targeted biopsy). In turn, this improved Gleason accuracy.

Need for standardization

As new parameters were integrated into prostate imaging, concern arose over “excessive variation in the performance, interpretation, and reporting of prostate MRI exams.”[i] In order to gain consistency, the European Society of Urogenital Radiology (ESUR) constructed interpretation and reporting guidelines that included the first version of the 5-level system, published in 2012 as PI-RADSv1. Soon, inconsistencies and limitations appeared, so in December, 2014 a second version was released (PI-RADSv2). While it tightened up the first version, over the next few years a few more flaws showed up. Therefore, an international PI-RADS Steering Committee was assembled with a goal of arriving at a consensus version that offered guidance while remaining flexible to accommodate future developments. The result is PI-RADSv2.1.

Taking consistency to a new level: PI-RADS v2.1

On March 27, 2019 the American College of Radiology published an online press release:

PI-RADS, now in its third iteration, has been adopted worldwide as the foundation for the acquisition, interpretation and reporting of prostate MRI exams performed to detect and diagnose prostate cancer. The updated version, PI-RADS v2.1, introduces several modifications while maintaining the original framework of assigning scores to individual imaging sequences and using these scores to derive, on a lesion by lesion basis, an overall likelihood that an abnormal area in the prostate represents clinically significant prostate cancer. It is anticipated that the adoption of PI-RADS v2.1 modifications will reduce inter-reader variability and strengthen reporters’ confidence in assigning a PI-RADS score to any lesion.

PI-RADS v2.1 revises the following:

• Technical Specifications for T2W, DWI, and DCE sequences
• Clarification in Measurement of Prostate Volume
• Revised Anatomical Sector Map
• Clarification in Interpretation Criteria for Central Zone (CZ) and Anterior Fibromuscular Stroma (AFS), Transition Zone (TZ) – what to score and how to score.
• Revision of criteria for DWI scores 2 & 3
• Clarification of distinction between (+) and (-) DCE d
• Discussion of bi-parametric MRI (mpMRI) where DCE sequences are omitted.[ii]

All of us at the Sperling Prostate Center are excited about how this latest PI-RADS version will enhance communication between clinical/academic centers, and between doctor and patient. PI-RADSv2.1 will reinforce the role of mpMRI in detecting, diagnosing and treating PCa to serve patients better.

NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.

References

[i] PI-RADS® Prostate Imaging – Reporting and Data System. Version 2.1. American College of Radiology. 2019. [ii] PI-RADS Steering Committee Releases New Version of the Prostate Imaging Reporting and Data System (v2.1 2019). American College of Radiology, press release dated Mar. 27, 2019. https://www.acr.org/Media-Center/ACR-News-Releases/2019/PIRADS-Steering-Committee-Releases-New-Version-2point1