Expect the unexpected: investigating discordant prostate MRI and biopsy results

Abstract

Objectives: To evaluate discrepant radio-pathological outcomes in biopsy-naïve patients undergoing prostate MRI and to provide insights into the underlying causes. Materials and Methods: A retrospective analysis was conducted on 2,780 biopsy-naïve patients undergoing prostate MRI at a tertiary referral centre between October 2015 and June 2022. Exclusions criteria were biopsy not performed, indeterminate MRI findings (PI-RADS 3) and clinically insignificant PCa (Gleason score 3+3). Patients with discrepant findings between MRI and biopsy results were categorized into two groups: MRI-negative/Biopsy-positive and MRI-positive/Biopsy-negative (biopsy-positive defined as Gleason score ≥ 3+4). An expert uroradiologist reviewed discrepant cases, retrospectively re-assigning PI-RADS scores, identifying any missed MRI targets and evaluating the quality of MRI scans. Potential explanations for discrepancies including MRI overcalls (including known pitfalls), benign pathology findings, and biopsy targeting errors. Results: Patients who did not undergo biopsy (n=1,258), or with indeterminate MRI findings (n=204), and clinically insignificant PCa (n=216) were excluded, with a total of 1,102 patients analysed. Of these, 32/1,102 (3%) were classified as MRI-negative/Biopsy-positive, and 117/1,102 (11%) as MRI-positive/Biopsy-negative. In the MRI-negative/Biopsy-positive group, 44% of studies were considered non-diagnostic quality. Upon retrospective image review, target lesions were identified in 28% of cases. In the MRI-positive/Biopsy-negative group, 42% of cases were considered to be MRI overcalls, 32% had an explanatory benign pathology finding, with biopsy targeting errors accounting for 11% of cases. Conclusion: Prostate MRI demonstrated a high diagnostic accuracy, with low occurrences of discrepant findings as defined. Common reasons for MRI-positive/Biopsy-negative cases included explanatory benign pathology findings and MRI overcalls.