PI-RADS: Where Next?

Abstract

Prostate MRI plays an important role in the clinical management of localized prostate cancer, mainly assisting in biopsy decisions and guiding biopsy procedures. The Prostate Imaging Reporting and Data System (PI-RADS) has been available to radiologists since 2012, with the most up-to-date and actively used version being PI-RADS version 2.1. This review article discusses the current use of PI-RADS, including its limitations and controversies, and summarizes research that aims to improve future iterations of this system.

Graphical abstract

Figure 1:

Images in a 70-year-old man with a serum prostate-specific antigen level of 6.8 ng/mL. (A) Axial T2-weighted MRI scan shows a focal hypointense lesion in the right apical peripheral zone (arrow). (B) Apparent diffusion coefficient map and (C) diffusion-weighted image with a b value of 1500 sec/mm² show a lesion with diffusion restriction with prominent hypointense and hyperintense signal features (arrows), and (D) dynamic contrast-enhanced (DCE) MRI scan shows focal early enhancement (arrow). The T2-weighted imaging, diffusion-weighted imaging, DCE MRI, and overall Prostate Imaging Reporting and Data System (PI-RADS) scores of this lesion were 4, 4, positive, and 4, respectively. Transrectal US/MRI fusion–guided biopsy with a transperineal approach revealed Gleason 3+4 prostate cancer with cribriform pattern within this PI-RADS category 4 lesion.

Figure 2:

Images in a 68-year-old man with a prostate-specific antigen level of 21.8 ng/mL and a prior negative prostate biopsy. (A) Axial and (B) sagittal T2-weighted MRI scans show a lesion in the midline anterior transition zone at the mid gland, with intermediate to high signal intensity and anterior extraprostatic extension (arrows). (C) The apparent diffusion coefficient map shows diffusion restriction with moderately hypointense signal (arrow) within the lesion, while the (D) diffusion-weighted image with a high b value of 1400 sec/mm² shows moderately hyperintense signal (arrow); the (E) dynamic contrast-enhanced MRI scan shows corresponding early arterial enhancement (arrow). The signal intensity of the lesion at T2-weighted MRI is higher than expected for typical prostate adenocarcinoma, but because of the extraprostatic extension findings, the lesion was assigned a T2-weighted MRI and an overall Prostate Imaging Reporting and Data System score of 5. MRI-targeted biopsy of the lesion revealed Gleason 4+4 prostate cancer with predominate cribriform morphology.

Figure 3:

Images in a 78-year-old man with a serum prostate-specific antigen level of 10 ng/mL. (A) Axial T2-weighted MRI scan shows a well-encapsulated nodule in the right mid peripheral zone (arrow), which suggests an ectopic benign prostatic hyperplasia nodule. (B) The apparent diffusion coefficient map and (C) diffusion-weighted image with a b value of 1500 sec/mm² show the nodule with diffusion restriction with prominent hypointense and hyperintense signal features (arrows), and the (D) dynamic contrast-enhanced (DCE) MRI scan shows focal early enhancement (arrow). The T2-weighted imaging, diffusion-weighted imaging, DCE MRI, and overall Prostate Imaging Reporting and Data System scores of this lesion were 2, 5, positive, and 5, respectively. Transrectal US/MRI–fusion guided biopsy revealed Gleason 4+4 prostate cancer within this lesion.

Figure 4:

Images in a 74-year-old man with a serum prostate-specific antigen level of 12.9 ng/mL. (A) Axial T2-weighted MRI scan, (B) apparent diffusion coefficient map, and (C) diffusion-weighted image with a b value of 1500 sec/mm² demonstrate no focal lesion within the prostate gland. (D) Dynamic contrast-enhanced MRI scan shows a very subtle linear enhancement in the right mid peripheral zone (arrow). Overall, the multiparametric MRI examination was negative for a cancer-suspicious lesion according to the Prostate Imaging Reporting and Data System. (E) Axial fluorine 18 DCFPyL PET/CT image demonstrates bilateral uptake (greater on the right side) in the prostate (arrows). Prostate biopsy revealed Gleason 4+3 prostate cancer within the right mid peripheral zone. DCFPyL = 2-(3-{1-carboxy-5-[(6-¹⁸F-fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid).

Figure 5:

Images in a 61-year-old man with a serum prostate-specific antigen level of 8 ng/mL. (A) Axial T2-weighted MRI scan shows a large homogeneously hypointense lesion in the entire left peripheral zone (arrows). (B) The apparent diffusion coefficient map shows the lesion with mild to moderate diffusion restriction (arrows), and the (C) dynamic contrast-enhanced MRI scan shows focal early enhancement (arrows). The overall Prostate Imaging Reporting and Data System score of this lesion was 5. Transrectal US/MRI fusion–guided biopsy revealed chronic granulomatous prostatitis secondary to tuberculosis within this lesion.

Figure 6:

Images in a 59-year-old man with a prostate-specific antigen level of 2.9 ng/mL and a prior negative prostate biopsy. (A) Axial T2-weighted MRI scan shows a subtle, noncircumscribed, moderately hypointense focus in the left base posteromedial peripheral zone (arrow) (T2-weighted MRI Prostate Imaging Reporting and Data System [PI-RADS] score of 3). On the (B) axial diffusion-weighted image with a high b value (1400 sec/mm²), the lesion has ill-defined mildly hyperintense signal (arrow), and on the (C) apparent diffusion coefficient (ADC) map, it has markedly hypointense signal (arrow) (diffusion-weighted imaging and ADC PI-RADS score of 3). On the (D) dynamic contrast-enhanced (DCE) MRI scan, the lesion shows early contrast enhancement (arrow) (DCE MRI PI-RADS score of positive). The final assessment category assigned was PI-RADS category 4. The focal abnormality was not identified at the time of the MRI interpretation by a novice reader, who assigned PI-RADS category 2 to the examination. Upon review of the images by a more experienced reader, the lesion was identified, and an MRI-targeted biopsy of the lesion revealed prostate cancer with a Gleason score of 3+4.

Figure 7:

Images in a 72-year-old man with a serum prostate-specific antigen level of 8.95 ng/mL. (A) Axial T2-weighted MRI scan shows a focal hypointense lesion in the left apical–mid anterior peripheral zone (arrow). (B) Apparent diffusion coefficient map and (C) diffusion-weighted image with a b value of 1500 sec/mm² show the lesion with mild to moderate diffusion restriction (arrows). (D) Biparametric MRI–based artificial intelligence model’s binary prediction map overlaid on the T2-weighted MRI scan automatically segments the prostate gland (blue shading) and detects the same lesion that was shown in other sequences (arrow; red shading). Transrectal US/MRI fusion–guided biopsy revealed Gleason 3+4 prostate cancer within this lesion.

Figure 8:

Images in a 65-year-old man with a prostate-specific antigen level of 3.4 ng/mL and no prior biopsy. (A) Axial T2-weighted MRI scan shows a 0.6-cm focal lesion with hypointense signal in the right mid posteromedial peripheral zone (arrow) (T2-weighted MRI Prostate Imaging Reporting and Data System [PI-RADS] score of 4). (B) Axial diffusion-weighted image with a high b value of 1400 sec/mm² shows susceptibility artifacts from rectal gas (arrow), causing geometric distortion that makes it difficult to categorize the lesion. (C) The apparent diffusion coefficient map shows the lesion with a markedly hypointense signal (arrow), and it is not as distorted as at diffusion-weighted imaging. (D) Dynamic contrast-enhanced (DCE) MRI scan shows early focal contrast enhancement within this lesion (arrow) (DCE MRI PI-RADS score of positive). The DCE image helped confirm the finding on the T2-weighted image and assign a final assessment category, since at least two of the three sequences must have sufficient diagnostic quality to give a Prostate Imaging Reporting and Data System score. MRI-targeted biopsy of the lesion revealed prostate cancer with a Gleason score of 3+4.