Noncontrast Multiparametric MRI Adds Value to Preoperative Peritoneal Cancer Index Assessment in Pseudomyxoma Peritonei: Comparison with Contrast-enhanced CT

Abstract Purpose To compare noncontrast multiparametric MRI (mpMRI) and contrast-enhanced CT (CECT) for agreement with intraoperative peritoneal cancer index (PCI) and detection of key imaging features in pseudomyxoma peritonei (PMP). Materials and Methods This retrospective study included 40 patients with pathologically confirmed PMP who underwent cytoreductive surgery and preoperative mpMRI and CECT in 2024. Intraoperative PCI across 13 abdominopelvic regions served as the reference standard. Total PCI agreement was assessed using intraclass correlation coefficients (ICCs) and Bland–Altman 95% limits of agreement (LoA), with analyses stratified by PCI (≤ 20 vs > 20). Regional agreement and sensitivities for key imaging features were also compared. Results Forty patients (median age, 60 years; 25 women) were included. mpMRI showed greater agreement with intraoperative total PCI than CECT (ICC, 0.98 vs 0.90; difference, 0.08 [95% CI: 0.05, 0.15]), with narrower LoA (7.1 vs 19.1 points). Agreement remained greater with mpMRI for PCI ≤ 20 (ICC, 0.91 vs 0.58) and PCI > 20 (ICC, 0.95 vs 0.74). mpMRI showed higher regional agreement in 11 of 13 regions after multiple-comparison correction. mpMRI had higher sensitivity for mucinous ascites (100% vs 61%; P = 0.002) and intralesional septation (95% vs 37%; P = 0.002), whereas CECT had higher sensitivity for intralesional calcification (100% vs 0%; P = 0.021). Conclusion Noncontrast mpMRI showed greater agreement with intraoperative PCI than CECT and higher sensitivity for mucinous ascites and intralesional septation, whereas CECT better detected intralesional calcification.