Value of ductal obstruction sign in the differentiation of benign and malignant breast lesions at MR imaging.

PURPOSE: MR-Mammography (MRM) is regarded as the most sensitive method for detection of breast cancer without a broad consensus on specificity. There is room for improvement of the existing ACR BIRADS lexicon by adding new and specific descriptors. Dilated ducts have been described in association with papillomas. However, the differential diagnostic value of this finding has not been investigated yet.

MATERIALS AND METHODS: 316 consecutive patients, undergoing histopathologic workup after MR-Mammography were included in this prospective, ethical review board approved study. Two blinded radiologists rated the images in consensus. Ductal obstruction was defined as dilated liquid filled ducts proximal an enhancing lesion. Sensitivity, specificity as well as positive and negative likelihood ratio (LR+, LR-) were calculated.

RESULTS: Dilated ducts were found in 60 cases (19%), 20 of these showed an association with enhancing lesions and were categorized as ductal obstruction (6.3%). Malignancy was found in two cases (one invasive ductal carcinoma and one DCIS) and benign tissue in 18 cases (15 papillomas). The difference of ductal obstruction between these groups was found to be highly significant in two-sided Fisher's exact test (p<0.001). Because of the clear association with benign lesions, benign lesions showing ductal obstruction were characterized as true positive findings. Therefore, following diagnostic parameters were calculated: sensitivity 15.4%, specificity 99.0%, LR+ 15.3, LR- 0.9.

DISCUSSION: If ductal obstruction is found to be positive, the associated lesion is most likely benign. Therefore, though a rare finding, this descriptor should be taken into account for improved lesion differentiation.