Characteristics of undetected prostate cancer on diffusion-weighted MR Imaging at 3-Tesla with a b-value of 2000 s/mm2: Imaging-pathologic correlation

Objective: To assess the accuracy of Diffusion-Weighted MR Imaging (DW-MRI) at 3-Teslas (3 T) with a b-value of 2000 s/mm(2) (b-2000 DW-MRI) to detect prostate cancer (PCa) and to describe the histological features of missed tumors. Methods: Prior to radical prostatectomy, 35 patients with a mean age of 64 +/- 6.2 years old [51-77 years old] had a b-2000 DW-MRI at 3-T, without rectal coil (acquisition time: 2 min, 15 s), and were analysed on an eight-sector basis by two independent readers blinded to the rest of the multiparametric-MRI protocol. Pathological tumor foci were matched with high intensity focal areas on MRI and correlated for Gleason score, sector location and largest axial diameter. Results: Of the 280 sectors analysed, histology showed PCa in 113 (113/280, 40%). Overall DW-MRI sensitivity, specificity and accuracy for tumor detection were 79-81%, 99-95% and 92-82% for readers 1 and 2, respectively (kappa test: 0.78). Of all, 28 (28/113, 25%) and 22 (22/113,20%) tumor foci were not detected by reader 1 and 2 respectively. These undetected tumor foci had a mean pathological axial axis of 5 mm (range: 3-15 mm) and a Gleason score of 6, 7( 3 + 4), 7 (4 + 3) and > 7 in 15/28 (54%), 9/28 (32%), 3/28 (10%) and 1/28 (4%) of cases for reader 1, and in 11 (50%), 5 (23%), 5 (23%) and 1 (4%) of cases for reader 2. Conclusion: A normal b-2000 DW-MRI at 3-T may miss small tumors without or with a minor Gleason 4 component. (C) 2015 Editions francaises de radiologie. Published by Elsevier Masson SAS. All rights reserved.