To determine whether abdominal and pelvic magnetic resonance imaging (MRI) with diffusion-weighted and dynamic gadolinium-enhanced imaging can be used to accurately calculate the peritoneal cancer index (PCI) before surgery compared to the PCI tabulated at surgery.

Thirty-three patients underwent preoperative MRI followed by cytoreductive surgery for primary tumors of the appendix (n = 25), ovary (n = 5), colon (n = 2), and mesothelioma (n = 1). MRIs were retrospectively reviewed to determine the MRI PCI. These scores were then compared to PCI tabulated at surgery. Patients were categorized as having small-volume tumors (PCI 0–9), moderate-volume tumors (PCI 10–20), and large-volume tumors (PCI > 20). The respective anatomic site scores for both MRI and surgery were compared.

There was no significant difference between the MRI PCI and surgical PCI for the 33 patients (P = 0.12). MRI correctly predicted the PCI category in 29 (0.88) of 33 patients. Compared to surgical findings, MRI correctly predicted small-volume tumor in 6 of 7 patients, moderate-volume tumor in 3 of 4 patients, and large-volume tumor in 20 of 22 patients. MRI and surgical PCI scores were identical in 8 patients (24%). A difference of <5 was noted in 16 patients (49%) and of 5–10 in 9 patients (27%). Compared to surgical-site findings, MRI depicted 258 truly positive sites of peritoneal tumor, 35 falsely negative sites, 35 falsely positive sites, and 101 truly negative sites, with a corresponding sensitivity of 0.88, specificity of 0.74, and accuracy of 0.84.

Combined diffusion-weighted and gadolinium-enhanced peritoneal MRI accurately predicts the PCI before surgery in patients undergoing evaluation for cytoreductive surgery.