Structured approach to resolving discordance between PI-RADS v2.1 score and targeted prostate biopsy results: an opportunity for quality improvement

Abstract

Background: Prostate multiparametric magnetic resonance imaging (mpMRI) can identify lesions within the prostate with characteristics identified in Prostate Imaging Reporting and Data System (PI-RADS) v2.1 associated with clinically significant prostate cancer (csPCa) or Gleason grade group (GGG) ≥ 2 at biopsy.

Objective: To assess concordance (PI-RADS 5 lesions with csPCa) of PI-RADS v2/2.1 with targeted, fusion biopsy results and to examine causes of discordance (PI-RADS 5 lesions without csPCa) with aim to provide a structured approach to resolving discordances and develop quality improvement (QI) protocols.

Methods: A retrospective study of 392 patients who underwent mpMRI at 3 Tesla followed by fusion biopsy. PI-RADS v2/2.1 scores were assigned to lesions identified on mpMRI and compared to biopsy results expressed as GGG. Positive predictive value (PPV) of PI-RADS v2/2.1 was calculated for all prostate cancer and csPCa. Discordant cases were re-reviewed by a radiologist with expertise in prostate mpMRI to determine reason for discordance.

Results: A total of 521 lesions were identified on mpMRI. 121/521 (23.2%), 310/524 (59.5%), and 90/521 (17.3%) were PI-RADS 5, 4, and 3, respectively. PPV of PI-RADS 5, 4, and 3 for all PCa and csPCa was 0.80, 0.55, 0.24 and 0.63, 0.33, and 0.09, respectively. 45 cases of discordant biopsy results for PI-RADS 5 lesions were found with 27 deemed "true" discordances or "unresolved" discordances where imaging re-review confirmed PI-RADS appropriateness, while 18 were deemed "false" or resolved discordances due to downgrading of PI-RADS scores based on imaging re-review. Adjusting for resolved discordances on re-review, the PPV of PI-RADS 5 lesions for csPCa was deemed to be 0.74 and upon adjusting for presence of csPCa found in cases of unresolved discordance, PPV rose to 0.83 for PI-RADS 5 lesions.

Conclusion: Although PIRADS 5 lesions are considered high risk for csPCa, the PPV is not 100% and a diagnostic dilemma occurs when targeted biopsy returns discordant. While PI-RADS score is downgraded in some cases upon imaging re-review, a number of "false" or "unresolved" discordances were identified in which MRI re-review confirmed initial PI-RADS score and subsequent pathology confirmed presence of csPCa in these lesions.

Clinical impact: We propose a structured approach to resolving discordant biopsy results using multi-disciplinary re-review of imaging and archived biopsy strikes as a quality improvement pathway. Further work is needed to determine the value of re-biopsy in cases of unresolved discordance and to develop robust QI systems for prostate MRI.

Keywords: Multiparametric prostate MRI; PI-RADS v2; Prostate cancer; Quality improvement.