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 in patients 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 >or=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 kappa 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.