Risk Stratification of Equivocal Lesions on Multiparametric Magnetic Resonance Imaging of the Prostate

Abstract

We systematically analyzed the records of patients with PI-RADS™ (Prostate Imaging Reporting and Data System) 3 lesions, which are called equivocal according to PI-RADS version 2, using prostate multiparametric magnetic resonance imaging and magnetic resonance imaging targeted biopsies. Systematic transrectal ultrasound guided biopsies served as the reference standard. A total of 120 consecutive patients were retrospectively included in the study. In these patients the overall PI-RADS score was 3 after 3 Tesla T2-weighted imaging, diffusion weighted imaging and dynamic contrast enhanced multiparametric magnetic resonance imaging as well as subsequent targeted magnetic resonance imaging/ultrasound fusion guided biopsies plus systematic 12-core transrectal ultrasound guided biopsies. The study end points were the prostate cancer detection rate, the Gleason score distribution, the prostate cancer location and risk stratification by subgroup analyses. Prostate cancer was detected in 13 of 118 patients for a detection rate of 11%, including 5 patients (4.2%) with a Gleason score of 3 + 4 = 7 or greater. Three of the 212 lesions (1.4%) in the transition zone and 6 of the 64 (9.4%) in the peripheral zone were positive for prostate cancer. Multiparametric magnetic resonance imaging revealed patterns of peripheral prostatitis combined with diffuse stromal hyperplasia in 54% of the patients with prostate cancer. Prostate volume was significantly lower in patients with prostate cancer (p = 0.015) but differences in prostate specific antigen levels were not statistically significant (p= 0.87). Prostate specific antigen density was higher in patients with prostate cancer (0.19 vs 0.12 ng/ml/ml). Low grade prostate cancer (Gleason score 3 + 3 = 6) can develop in patients with an overall PI-RADS score of 3. Prostate cancer with a Gleason score of 3 + 4 = 7 or greater can be detected by multiparametric magnetic resonance imaging with a high degree of certainty. Gleason score 4 + 3 = 7 or greater prostate cancer is unlikely in PI-RADS 3 lesions. Therefore, these patients should primarily undergo followup multiparametric magnetic resonance imaging. In patients with a combination of multiparametric magnetic resonance imaging aspects of extensive prostatitis and diffuse stromal hyperplasia low prostate volume and/or high prostate specific antigen density biopsy might be considered.