Rare breast neoplasms: is there any peculiar feature on magnetic resonance mammography?

PURPOSE: The purpose of this study is to describe the semiological features of rare breast neoplasms at magnetic resonance mammography (MRM). MATERIALS AND METHODS: Out of 468 MRMs of patients with a histological diagnosis of breast malignancy, 27 (5.7%) cases of rare breast neoplasms, confirmed by definitive histological analysis on surgical specimens, were selected: four (0.9%) intracystic papillary neoplasms, four (0.9%) intraductal papillary neoplasms, five (1.0%) invasive papillary neoplasms, two (0.4%) medullary carcinomas, seven (1.5%) mucinous carcinomas, three (0.6%) tubular carcinomas, one (0.2%) tubulo-lobular carcinoma and one (0.2%) desmoid tumour. Two radiologists evaluated the MRM images according to Fischer criteria and indicated a level of diagnostic suspicion. In particular, MRM lesion morphology and enhancement characteristics were analysed. RESULTS: No semiologic features of malignancy or peculiar appearances indicating rare breast neoplasm were identified. On the contrary, MRM appearance was nonspecific and often suggestive of probably benign (Breast Imaging Reporting and Data System-BI-RADS 3) (40%) or benign lesions (BI-RADS 2) (7.5%), or lesions were undetectable at MRM (BI-RADS 1) (7.5%). CONCLUSIONS: Frequently, rare breast neoplasms show low suspicious morphologic and kinetic patterns at MRM, and they are often classified as indeterminate lesions. This is probably due to their high grade of differentiation and their histological features.