The PIRADS v2.1 Classification: A Guide for Reading and Interpretation

The Prostate Imaging Reporting and Data System (PIRADS) is a cornerstone of modern prostate cancer diagnostics, standardizing the acquisition, interpretation, and reporting of multiparametric Magnetic Resonance Imaging (mpMRI). This article provides a comprehensive guide to PIRADS version 2.1, detailing its structured algorithm for assigning a risk score from 1 to 5 that correlates with the likelihood of clinically significant prostate cancer (csPCa). We explain the zone-dependent rules, sequence-specific criteria, and key improvements of v2.1, including its refined transition zone assessment. Furthermore, we contextualize its clinical impact with current evidence and discuss emerging trends, such as biparametric MRI and artificial intelligence, that are shaping the future of prostate imaging.