Mucinous appendiceal neoplasms: preoperative MR staging and classification compared with surgical and histopathologic findings.

OBJECTIVE The objective of our study was to determine the accuracy of MRI in the preoperative staging and classification of mucinous appendiceal neoplasms and to describe the MRI features that are useful for selecting patients for surgical resection. MATERIALS AND METHODS Twenty-two patients underwent preoperative MRI including T1-weighted, T2-weighted, immediate gadolinium-enhanced, and delayed gadolinium-enhanced imaging. Two observers reviewed the images for peritoneal tumor at 13 sites, tumor size and distribution, and degree of tumor enhancement. Peritoneal tumor sites were recorded at surgery. Cytoreduction was categorized as complete or suboptimal. Surgical specimens were classified as disseminated peritoneal adenomucinosis tumors, intermediate-grade tumors, or peritoneal mucinous carcinomatosis tumors. RESULTS Surgery confirmed 232 tumor sites. Delayed gadolinium-enhanced MRI was the most accurate of the MR techniques, with a sensitivity, specificity, and accuracy of 89%, 87%, and 89%, respectively, for observer 1 and 82%, 87%, and 83% for observer 2 (p < 0.001). Surgical cytoreduction was complete in 14 patients and suboptimal in eight. MRI findings predicting suboptimal cytoreduction included a large (> 5 cm) mesenteric mass, which was present in 75% of the patients in the suboptimal cytoreduction group and 0% of those in the complete cytoreduction group; diffuse mesenteric tumor (88% and 0%, respectively); tumor encasement of mesenteric vessels (88% and 0%); or diffuse small-bowel serosal tumor (75% and 0%). Histopathology results showed six disseminated peritoneal adenomucinosis tumors, four intermediate tumors, and 11 peritoneal mucinous carcinomatosis tumors. The specimens for the remaining patient were not available for histopathologic analysis. Qualitatively, the 11 peritoneal mucinous carcinomatosis tumors showed greater enhancement than the liver, whereas six disseminated peritoneal adenomucinosis and the four intermediate tumors showed less enhancement than the liver. Quantitatively, the mean tumor-to-liver contrast for disseminated peritoneal adenomucinosis and intermediate tumors was 0.67 compared with 1.53 for peritoneal mucinous carcinomatosis tumors (p < 0.0001). CONCLUSION Of the MR techniques evaluated, delayed gadolinium-enhanced MRI was the most accurate for the staging and classification of mucinous appendiceal neoplasms and provided prognostic information useful for patient selection.