Accuracy in differentiation of mucinous and nonmucinous rectal carcinoma on MR imaging

Purpose: The purpose of this work was to determine the diagnostic accuracy of MRI for the differentiation of mucinous and nonmucinous carcinomas inpatients with rectal carcinomas. Method: Seventy-six patients with pathologically proven rectal adenocarcinomas were evaluated with MRI. Both T2-weighted fast spin echo and T1-weighted spin echo images were independently reviewed by two radiologists who were blinded for tumor histology. Of the 76 cases, mucin pools were found in 28 (37%), and 16 had a mucin pool occupying greater than or equal to 50% of the tumor (mucinous carcinoma). The sensitivity, specificity, accuracy, and positive and negative predictive values of distinguishing between mucinous and nonmucinous carcinomas were calculated. The interobserver agreement was estimated using K statistics. Results: The accuracies of the diagnosis of mucinous carcinoma were 97% for Radiologist 1 and 96% for Radiologist 2. The sensitivities and specificities for diagnosing a mucinous carcinoma were 94 and 98% for Radiologist 1 and 100 and 95% for Radiologist 2, respectively. Interobserver agreement was good (kappa = 0.61) for the identification of a mucin pool and was excellent (kappa = 0.81) for the diagnosis of a mucinous carcinoma. Conclusion: Differentiation of mucinous and nonmucinous rectal carcinoma is highly accurate on preoperative MRI.