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

Purpose: 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.

Materials and methods: 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.

Results: 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).

Conclusions: 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.