PI-RADS version 2.1 for the evaluation of transition zone lesions: a practical guide for radiologists

Abstract

Multiparametric MRI has been established as the most accurate non-invasive diagnostic imaging tool for detecting prostate cancer (PCa) in both the peripheral zone and the transition zone (TZ) using the PI-RADS (Prostate Imaging Reporting and Data System) v. 2.1 released in 2019 as a guideline to reporting. TZ PCa remains the most difficult to diagnose due to a markedly heterogeneous background and a wide variety of atypical imaging presentations as well as other anatomical and pathological processes mimicking PCa. The aim of this paper was to present a spectrum of PCa in the TZ, as a guide for radiologists.

Figure 1.

Normal transition zone. Multiple similar appearing nodules on the T₂ weighted sequence (a) corresponding to multiple foci of hypointensity on the ADC map (b), without significant hyperintensity on the DWI image (c), scattered throughout the transition zone are common findings in benign prostatic hypertrophy and should not be scored. ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging.

Figure 2.

PI-RADS 1 category – Normal transition zone. a) Axial T ₂ weighted sequence: homogeneous intermediate signal intensity tissue and multiple round, completely encapsulated nodules defined as “typical nodules” with no focal area of significant restricted diffusion on ADC map (b) and DWI image (c).Typical nodules may show focal hyperenhancement on the DCE image (d). The coronal T ₂ weighted sequence (e) confirm the typical capsulated appearance of nodules. ADC, apparent diffusion coefficient; DCE, dynamic contrast enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 3.

PI-RADS 1 category – Normal transition zone. (a) Axial T ₂ weighted sequence: multiple pseudo ill-defined nodules (arrows) with variable degrees of diffusion restriction on the ADC map (arrows in b) but without significant hyperintensity on the DWI image (arrows in c). The nodules may show focal hyperenhancement on DCE image (arrows in d). On the coronal (e) and sagittal (f) T ₂ weighted images the nodules appear completely encapsulated (arrows). ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 4.

PI-RADS 2 category – normal transition zone. (a) Axial T ₂ weighted sequence: a mostly encapsulated nodule defined as an “atypical nodule” (arrow) with mild inhomogeneous hypointensity on the ADC map (arrow in b) and no significant hyperintensity on DWI image (c). The nodule shows focal hyperenhancement on the DCE image (arrow in d). The coronal (e) and sagittal (f) T ₂ weighted images can help to identify the capsule of the nodule (arrows). This nodule is proved to be benign prostatic tissue at the fusion targeted biopsy and remained stable after 2 years follow-up with mpMRI. ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 5.

PI-RADS 3 category – prostate cancer with Gleason Score 3 + 4 (at fusion targeted biopsy). (a) Axial T ₂ weighted sequence: two mostly encapsulated hypointense nodules (atypical nodules) in the left mid prostate (arrows). (b) ADC map and (c) high b-value DWI image: restricted diffusion within the nodules (arrows) is much greater than the background. (d) DCE image: the nodules show focal hyperenhancement. At the fusion targeted biopsy, three samples were carried out in each nodule with the same histopathological finding. ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 6.

PI-RADS 3 category – prostate cancer with Gleason Score 3 + 4 (at fusion targeted biopsy). (a) Axial T ₂ weighted sequence: hypointense tissue between nodules with irregular margins in the right mid prostate (arrow) with restricted diffusion greater than the background on the ADC map (arrow in b) corresponding to an hyperintensity on the DWI image (arrow in c); focal hyperenhancement can be seen on the DCE image (arrow in d). (e) The irregular margins of the neoplastic tissue are clearly depicted on the coronal T ₂ weighted sequence (arrow). ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 7.

PI-RADS 3 category – normal stromal tissue (at fusion targeted biopsy). (a) Axial T ₂ weighted sequence: hypointense area with irregular margins within an encapsulated nodule (arrow) with restricted diffusion greater than the background on the ADC map (arrow in b) and no focal hyperenhancement on the DCE image (c). These features of “nodule in the nodule” typically correspond to stromal tissue within a nodule of benign prostatic hypertrophy, as well depicted also in the sagittal plane (arrow in d) and may show irregular margins and focal marked diffusion restriction. This finding should be correctly scored as PI-RADS 2. ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 8.

PI-RADS 4 category – prostate cancer with Gleason Score 4 + 3 (at fusion targeted biopsy). (a) Axial T ₂ weighted sequence: non-circumscribed, homogeneous hypointensity, with irregular ill-defined margins and <1.5 cm in greatest dimension, in the apical anterior site (arrow) with marked restricted diffusion on the ADC map (arrow in b) and on the high b-value DWI image (arrow in c). The DCE shows weak focal enhancement of the lesion (arrow in d). ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 9.

PI-RADS 5 category – prostate cancer with Gleason Score 3 + 4 (at fusion targeted biopsy). (a) Axial T ₂ weighted sequence: homogeneous hypointense teardrop-shaped area with ill-defined margins, ≥1.5 cm in greatest dimension, in the anterior left site of the mid prostate (arrow) with marked restricted diffusion on the ADC map (arrow in b). ADC, apparent diffusion coefficient; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 10.

PI-RADS 5 category – prostate cancer with Gleason Score 4 + 4 (at fusion targeted biopsy). (a) Axial T₂ weighted sequence: ill-defined, lenticular, hypointense area in the anterior right site (arrow), with marked restricted diffusion on the ADC map (arrow in b) and on the DWI image (arrow in c), and very weak enhancement on the DCE image (arrow in d). (e) Coronal T₂ weighted sequence: the lesion clearly differs from the remaining transition zone (arrow). ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 11.

PI-RADS 5 category – prostate cancer with Gleason Score 4 + 4 and prevalent cribriform pattern (at fusion targeted biopsy). (a) Axial T ₂ weighted sequence: non-circumscribed, homogeneous hypointensity, ≥1.5 cm in greatest dimension, in the left side of the mid prostate (arrow) with marked restricted diffusion on the ADC map (arrow in b) and on the DWI image (arrow in c). The DCE shows marked hyperenhancement (arrow in d). On the coronal (e) and sagittal (f) T ₂ weighted sequence, the lesion corresponds to a thin hypointense band at the bottom of the transition zone (white arrows). The sagittal image also allows the correct anatomical attribution of the lesion, distinguishing the anterior lesion (white arrow) from the adjacent peripheral zone which is posterior and inferior (black arrow). ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 12.

Exacerbated prostatitis (at fusion targeted biopsy). (a) Axial T ₂ weighted sequence: ill-defined, lenticular shape hypointensity of the transition zone at the apex (arrow). (b) ADC map and (c) DWI image: restricted diffusion (arrows). (d) DCE image: marked diffuse hyperenhancement (arrow). At the post-biopsy re-evaluation, we can notice that the diffusion restriction is mild and heterogenous, and the hypervascularisation is much more evident. Nevertheless, this finding should be scored as a PI-RADS 4 lesion. ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted imaging; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 13.

Granulomatous prostatitis (at fusion targeted biopsy) in a patient having undergone previous intravesical Bacillus Calmette-Guérin therapy. (a) Axial T ₂ weighted sequence: inhomogeneous hypointensity of the peripheral and transition zone (arrowheads). (b) ADC map: restriction of the diffusivity (arrowheads). (c) DCE image: marked diffuse hyperenhancement (arrowheads). This finding was scored as a PI-RADS 5 lesion; however, after careful re-evaluation, one can see the marked hyperenhancement of the entire gland and surrounding tissue with hyperplasia of the veins of the periprostatic plexus; moreover, a small area of marked restricted diffusion (arrow in b) and avascularity with rim enhancement (arrow in c) can be seen; this area exhibits characteristics of necrosis and in this setting could correspond to “caseous necrosis”. Finally, the clinical history of the patient should help in reaching the correct diagnosis. ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; PI-RADS, Prostate Imaging Reporting and Data System.

Figure 14.

Adenosis (at fusion targeted biopsy). (a) Axial T₂ weighted sequence: ill-defined, lenticular, hypointense area in the right site (arrow), with restricted diffusion on the ADC map (arrow in b) and marked hyperenhancement on the DCE image (arrow in c). At the post-biopsy re-evaluation, we can notice that the diffusion restriction is mild and heterogenous, and the hypervascularisation is much more evident, as in the case of Figure 12. Nevertheless, this finding should be scored as a PI-RADS 4 lesion. ADC, apparent diffusion coefficient; DCE, dynamic contrast-enhanced; PI-RADS, Prostate Imaging Reporting and Data System