Characteristics of undetected prostate cancer on diffusion-weighted MR Imaging at 3-Tesla with a b-value of 2000s/mm(2): Imaging-pathologic correlation.

OBJECTIVE

To assess the accuracy of Diffusion-Weighted MR Imaging (DW-MRI) at 3-Teslas (3T) with a b-value of 2000s/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±6.2years old [51-77years old] had a b-2000 DW-MRI at 3-T, without rectal coil (acquisition time: 2min, 15s), 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 5mm (range: 3-15mm) 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.