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Prognostic value of Prostate Imaging and Data Reporting System (PI-RADS) v. 2 assessment categories 4 and 5 compared
Christopher S Lim1, Matthew D F McInnes1, Robert S Lim1
1Ottawa Hospital, University of Ottawa, Department of Radiology, Civic Campus C1, Ottawa, Ontario, Canada.
Purpose:
To assess Prostate Imaging and Data Reporting System (PI-RADS) v. 2 score 4/5 lesions compared to Gleason score (GS) and stage after radical prostatectomy (RP) and to validate the proposed 15-mm size threshold that differentiates category 4 versus 5 lesions.
Materials And Methods:
With Institutional Review Board (IRB) approval, 140 men underwent 3T magnetic resonance imaging (MRI) and RP between 2012-2015. Two blinded radiologists: 1) assigned PI-RADS v. 2 scores, 2) measured tumor size on axial T2 -weighted-MRI, and 3) assessed for extraprostatic extension (EPE). Interobserver agreement was calculated and consensus diagnoses achieved through reference standard (MRI-RP maps). PI-RADS v. 2 scores and tumor size were compared to GS and stage using chi-square, analysis of variance (ANOVA), and receiver operating characteristic (ROC) curve analysis.
Results:
In all, 80.7% (113/140) of tumors were category 4 (n = 45) or 5 (n = 68) lesions (κ = 0.45). Overall tumor size was 18.2 ± 7.7 mm and category 5 lesions were larger (22.6 ± 6.8 versus 11.5 ± 1.9 mm, P < 0.001). High-risk (GS ≥8) tumors were larger than low- and intermediate-risk tumors (P = 0.016) and were more frequently, but not significantly so, category 5 lesions (78.9% [15/19] vs. 22.1% [4/10], P = 0.18). 67.3% (76/113) of patients had EPE. Category 5 lesions were strongly associated with EPE (P < 0.0001). Area under the ROC curve for diagnosis of EPE by size was 0.74 (confidence interval 0.64-0.83), with size ≥15 mm yielding a sensitivity/specificity of 72.4/64.9%. Size improved sensitivity for diagnosis of EPE compared to subjective assessment (sensitivity/specificity ranging from 46.1-48.7%/70.3-86.5%, κ = 0.29) (P = 0.028).
Conclusion:
PI-RADS v. 2 category 5 lesions are associated with higher Gleason scores and EPE. A 15-mm size threshold is reasonably accurate for diagnosis of EPE with increased sensitivity compared to subjective assessment.
Level Of Evidence:
3 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:257-266.
