PI-RADS version 2: Standardized acquisition, interpretation, and reporting of prostate MRI [Classics Series]

This study summary is an excerpt from the book 2 Minute Medicine’s The Classics in Medicine: Summaries of the Landmark Trials

1. A joint steering committee have revised the original Prostate Imaging Reporting and Data System (PI-RADS) guidelines to form PI-RADS version 2 (v2), which improves the standardization of imaging acquisition and reporting in pre-therapy patients with suspected prostate cancer.

2. DWI is the predominant sequence to evaluate peripheral zone (PZ) lesions, while T2-weighted magnetic resonance imaging (MRI) is favored for evaluation of the transition zone (TZ).

3. Lesions with a PI-RADS score of 3 should be reported. If multiple, up to 4 should be reported with the index lesion identified.

4. The guidelines are intended to evolve as the prostate imaging community gains clinical experience in the application of PI-RADS v2.

Original Date of Publication: April 2015

Study Rundown: The European Society of Urogenital Radiology (ESUR) originally published the Prostate Imaging Reporting and Data System (PI-RADS) in 2012 to provide structured clinical guidelines for multiparametric prostate magnetic resonance imaging (mpMRI) using evidenced-based data and consensus expert opinion. This guideline was updated in 2015 by a steering committee formed by the American College of Radiology (ACR), ESUR, and AdMeTech Foundation to standardize and reduce the inter-center variability in imaging acquisition and reporting, and to improve characterization and risk stratification of patients undergoing imaging for suspected prostate cancer.

In the original version, prostatic abnormalities were scored based on individual pulse sequences on mpMRI; including T2-weighted, diffusion weighted imaging and apparent diffusion coefficient (DWI-ADC), dynamic contrast-enhanced (DCE) imaging, and (optionally) MR spectroscopy. Although the guidelines carried information regarding risk stratification, enrollment criteria for active surveillance programs, and recommendations for imaging protocols, it failed to specify how the individual sequences contributed to an overall score. This resulted in between-center variability in image acquisition and reporting.

Compared to the original version, PI-RADS v2 is more precise in its scope and purpose. It includes an overview of normal prostate anatomy, benign findings, terminology, and provides specific recommendations to assign an overall score. The following are several key differences between the original and PI-RADS v2:

• The guidelines are explicit that they only apply to pre-therapy patients being evaluated for prostate cancer, not for follow-up or post-treatment assessment.
• Only minimal technical parameters for acceptable mpMRI are given.
• MR spectroscopy is omitted and DCE is assigned a minor role.
• The overall score is based only on mpMRI, without contribution from clinical factors.

PI-RADS v2 has also defined the predominant sequence for evaluation, based on the zonal location of the abnormality; DWI for PZ lesions and T2-weighted MRI for TZ lesions. Other sequences are considered ancillary for equivocal lesions. DCE is no longer evaluated on a 5-point scale and is now either positive or negative. The 5-point scale used to evaluate DWI-ADC and T2-weighted MRI are retained from the original version. The score based on the predominant sequence is used for an overall score assignment and interpretation of cancer risk:

PI-RADS 1 – Very low (clinically significant cancer is highly unlikely to be present)

PI-RADS 2 – Low (clinically significant cancer is unlikely to be present)

PI-RADS 3 – Intermediate (the presence of clinically significant cancer is equivocal)

PI-RADS 4 – High (clinically significant cancer is likely to be present)

PI-RADS 5 – Very high (clinically significant cancer is highly likely to be present)

The following is the scoring classification for PZ and TZ lesions based on the appearance on ADC and high-b value DWI, PZ lesions based on T2-weighted MRI, and TZ lesions based on T2-weighted MRI, respectively. Please see Tables I and II for further detail:

PZ or TZ lesions based on DWI-ADC:

1. Normal on ADC maps or high-b value DWI
2. Indistinct hypointense abnormality on ADC
3. Focal mild to moderate hypointense abnormality on ADC and isointense to mild hyperintense on high-b value DWI
4. Focal markedly hypointense abnormality on ADC and markedly hyperintense on high-b value DWI; £5 cm in greatest dimension
5. Same as 4), but ³5 cm in greatest dimension or definite extraprostatic extension

PZ abnormalities based on T2-weighted MRI:

1. Uniformly hyperintense (normal)
2. Linear, wedge-shaped, or diffuse mild hypointensity, usually indistinct margin
3. Noncircumscribed, rounded, moderate hypointensity
4. Circumscribed, homogenous moderately hypointense focus or mass confined to the prostate; £5 cm in greatest dimension
5. Same as 4), but ³5 cm in greatest dimension or definite extraprostatic extension

TZ abnormalities based on T2-weighted MRI:

1. Homogenous intermediate signal intensity (normal)
2. Circumscribed hypointense or heterogenous encapsulated nodule(s)
3. Heterogenous signal intensity with obscured margins
4. Noncircumscribed, homogenous moderately hypointense focus or mass confined to the prostate; £5 cm in greatest dimension
5. Same as 4), but ³5 cm in greatest dimension or definite extraprostatic extension

A maximum of 4 lesions with an overall score of 3, 4, or 5 are reported, with the index lesion identified. A PI-RADS score is reported for each lesion. A standardized format for reporting is recommended, though no specific model is given. The guidelines are intended to evolve with time, as radiologists gain experience in the clinical application of the PI-RADS v2 system.

Click to read the PI-RADS v2 Consensus Statement

Hamoen EHJ, de Rooij M, Witjes JA, Barentsz JO, Rovers MM. Use of the Prostate Imaging Reporting and Data System (PI-RADS) for Prostate Cancer Detection with Multiparametric Magnetic Resonance Imaging: A Diagnostic Meta-analysis. Eur Urol. 2015 Jun;67(6):1112–21.

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