Multiparametric Magnetic Resonance Imaging (mpMRI) has a good diagnostic accuracy in detecting clinically significant prostate cancer (csPCa),
defined as Gleason Score (GS)≥3+4, with a negative predictive value ranging from 63% to 98% [1].
Currently,
mpMRI is frequently performed before prostate biopsy. According to the 2018 European Association of Urology (EAU) guidelines [2] mpMRI can either be used theoretically:
- to improve the diagnosis of csPCa by performing MRI-targeted biopsies in addition to standard systematic biopsies in patients with a positive mpMRI; patients with a negative mpMRI would undergo standard systematic biopsies;
- as a pre-biopsy triage test to perform only MRI-targeted biopsies in case of positive mpMRI findings; in patients with a negative mpMRI no prostate biopsy would be performed.
The Prostate Imaging Reporting and Data System version 2 (PI-RADSv2) standardizes image acquisition,
interpretation and mpMRI reports [3]. PI-RADSv2 has been validated and it is widely used in routine clinical practice although inter-reader reproducibility remains moderate [4-7].
MRI lesions are classified using a 5-point scale based on the probability of clinically significant cancer.
Table 1: PI-RADSv2 Assessment Categories
For the identification of peripheral zone (PZ) lesions diffusion-weighted imaging (DWI) is the main sequence,
by a qualitative interpretation of DWI signal intensity on high b-value and corresponding Apparent Diffusion Coefficient (ADC) map. Dynamic Contrast-Enhanced (DCE) imaging is the tie-breaker sequence to further characterize lesion that are initially considered indeterminate i.e.
PI-RADSv2 score 3 [3].
Table 2: PI-RADSv2 assessment for T2W
Table 3: PI-RADSv2 assessment for DWI
Table 4: PI-RADSv2 assessment for DCE
Table 5: PI-RADSv2 Assessment for Peripheral Zone (PZ)
Prostate cancer (PCa) prevalence increases with the PI-RADSv2 assessment category with a bioptic detection rate of 39%,
72% and 91% for all prostate cancers in PI-RADSv2 categories 3,
4 and 5 respectively [8]. The method has a good sensitivity whereas it has a relatively moderate specificity.
This is probably in part due to the qualitative evaluation of the images that could also reduce inter-reader reproducibility.
Many Authors have investigated the role of ADC values in differentiating between prostate cancer and normal tissue; an inverse correlation between ADC values and GS has also been observed [9,
10].
Some recent Studies have also analyzed the correlation of quantitative ADC measurements with PIRADSv2 [11,12] showing a possible role for ADC in assisting PIRADSv2 DWI classification,
thus improving PI-RADSv2 diagnostic performance.
The aim of this study is to evaluate the role of quantitative ADC measurement in the detection of prostate cancer in peripheral zone lesions with a PIRADSv2 score of 4,
using MRI/US fusion-guided targeted biopsy report as reference standard.
Particularly,
we focused on 4(3+1) lesions subgroup,
upgraded from 3 to 4 based on positive DCE imaging.