Detection of occult non-mass enhancement in bloody nipple discharge using US/MRI fusion imaging: a case report.

A 66-year-old woman presented with right bloody nipple discharge (BND). Initial evaluation, including palpation, mammography (MMG), ultrasonography (US), and cytology, revealed no abnormalities. In the second year, persistent BND prompted breast magnetic resonance imaging (MRI), which demonstrated non-mass enhancement in the lower right breast and was classified as Breast Imaging Reporting and Data System (BI-RADS) category 3; therefore, imaging surveillance was performed. In the third year, cytological examination revealed atypical cells. Repeat MRI again demonstrated non-mass enhancement. US/MRI fusion identified two suspicious regions; however, ultrasound-guided needle biopsy showed no evidence of malignancy. Because of persistent BND and cytological atypia, excisional biopsy was performed, and ductal carcinoma in situ (DCIS) was confirmed. US/MRI fusion may assist in localizing target areas for biopsy in patients with MRI-detected lesions without corresponding findings on MMG or US; however, histopathological confirmation remains essential.