Real-world performance of pelvic MRI and abdominopelvic CT for nodal staging in higher-risk prostate cancer and the incremental clinical value of CT

Abstract Background and Objective: Conventional imaging with pelvic magnetic resonance imaging (MRI) and abdominopelvic computed tomography (CT) is still used for staging of prostate cancer (PCa), particularly when molecular imaging is unavailable. mpMRI is currently recommended before prostate biopsy. We evaluated the agreement between MRI and CT for nodal and distant staging, their diagnostic accuracy against surgical nodal staging, and the real-world clinical utility of CT when pelvic MRI is already available. Methods: Among consecutive prostate biopsies, we retrieved patients with unfavorable intermediate- or high-risk PCa who underwent both pelvic MRI and abdominopelvic CT (and bone scan). Agreement for nodal staging was assessed using Cohen’s κ. Diagnostic performance was evaluated in patients undergoing radical prostatectomy with pelvic lymph node dissection, using final pathology as the reference standard. The clinical yield of CT was assessed post hoc, considering nodal or metastatic reclassification or urgent non-PCa-related findings. Key Findings and Limitations: We included 323 consecutive patients. MRI and CT identified cN1 disease in 6.8% and 8.1% of cases, respectively, and showed moderate agreement for pelvic nodal staging (κ = 0.51), with higher agreement in non-surgical patients. Both modalities demonstrated very low sensitivity for nodal metastases (≤ 20%) compared with pathology, with area under the curve (AUC) < 0.60. In the subgroup of patients with also molecular imaging available (n = 82) PSMA PET/CT showed superior performance (AUC = 0.86). MRI and CT (plus bone scan) showed moderate agreement for distant metastasis (κ = 0.56). CT provided clinically relevant information not detectable in mpMRI in 14.1% of patients (number needed to scan = 7). Limitations include the retrospective design and lack of centralized imaging review. Intervention: Imaging strategies were evaluated observationally. Conclusions and Clinical Implications: Pelvic MRI and CT show moderate agreement for nodal staging but poor diagnostic accuracy. Although the incremental value of CT beyond pelvic MRI is limited, it may still contribute to change management when PSMA PET/CT is unavailable.