Comparison of MRI and CT for predicting the Peritoneal Cancer Index (PCI) preoperatively in patients being considered for cytoreductive surgical procedures.

PURPOSE: To compare the accuracy of MRI and CT for predicting the Peritoneal Cancer Index (PCI) preoperatively compared with the PCI tabulated at surgery.

METHODS: Twenty-two patients underwent preoperative MRI and CT scanning followed by cytoreductive surgery for appendiceal (n = 17) and ovarian (n = 5) cancer. MR and CT examinations were retrospectively reviewed to determine the PCI. The results of these scores were compared with PCI tabulated at surgery. Patients were categorized as small volume tumor (PCI 0-9), moderate volume (PCI 10-20), and large volume (PCI > 20). Respective anatomic site scores for MRI and CT were compared with surgical findings.

RESULTS: Compared with surgical PCI, MRI correctly categorized tumor volume in 20 (0.91) of 22 patients, including 3 of 4 patients with small volume tumor, 2 of 2 patients with moderate volume tumor, and 15 of 16 patients with large volume tumor. CT correctly categorized tumor volume in 11 of 22 (0.50) patients, including 2 of 4 patients with small-volume tumor, 2 of 2 patients with moderate volume tumor, and 7 of 16 patients with large-volume tumor. In 19 of 22 patients, CT underestimated the volume of tumor found at surgery. For all patients, the median PCI score at surgery was 33 compared with 36 for MRI and 15 for CT. Surgery confirmed 222 sites of tumor. MRI demonstrated per site sensitivity of 0.95, specificity 0.70, and accuracy 0.88. CT showed a corresponding per site sensitivity 0.55, specificity 0.86, and accuracy 0.63.

CONCLUSIONS: MRI more accurately predicts PCI preoperatively in patients undergoing evaluation for cytoreductive surgery.