Correlation of Radiologic with Surgical Peritoneal Cancer Index Scores in Patients with Pseudomyxoma Peritonei and Peritoneal Carcinomatosis: How Well Can We Predict Resectability?

INTRODUCTION: Pseudomyxoma peritonei (PMP) and peritoneal carcinomatosis (PC) arises from primary or secondary peritoneal cancer and can be treated with complete surgical removal of disease. Suitability for surgery is based on a peritoneal cancer index (PCI), with a PCI ≥ 20 representing unresectable disease.

AIMS: Compare preoperative imaging with surgical findings based on PCI.

METHODS: All cases of patients with PMP and PC undergoing cytoreductive surgery ± hyperthermic intraperitoneal chemotherapy (HIPEC) between 2010 and 2014 were included. Two staff radiologists blinded to surgical PCI scores retrospectively reviewed imaging studies to calculate corresponding radiologic PCI scores for each patient. Correlation between radiologic PCI and surgical PCI, as obtained from operative reports, was assessed using Spearman's rho correlation coefficients. Preoperative assessment of a PCI cutoff of 20 on imaging was compared with actual surgical PCI using sensitivity, specificity, and positive and negative predictive values.

RESULTS: Forty-two patients had a mean surgical PCI ± SEM score of 15.1 ± 1.3 and mean radiologic PCI of 15.5 ± 1.5. The most common tumor histologies were appendiceal (60 %) and colon (33 %) adenocarcinoma and were of low tumor grade (67 %). Correlation between individual radiologists and surgical PCI was 0.59 and 0.62, respectively (all p < 0.001). When mean radiologic PCI was used, this correlation with surgical PCI improved to 0.64 and to 0.65 when good quality studies only were considered (all p < 0.001). Radiologic PCI score had a sensitivity of 76 %, a specificity of 69 %, positive predictive value of 85 %, and a negative predictive value of 56 % when compared with the surgical PCI. In patients with a radiologic PCI score ≥ 20, 6/13 (46 %) still achieved adequate cytoreduction.

CONCLUSIONS: Good quality cross-sectional imaging, combined with overreading and formal assessment of all components of the PCI score yields the best correlation with actual surgical findings. Although preoperative assessment of PCI ≥ 20 was reasonably accurate, using this cutoff to assess resectability is problematic as almost half of these patients were still able to undergo adequate cytoreduction. Better assessment of resectability is needed preop, either by refinement of the PCI criteria or routine staging laparoscopy.