Nonmalignant Breast Lesions: ADCs of Benign and High-Risk Subtypes Assessed as False-Positive at Dynamic Enhanced MR Imaging

Purpose: To evaluate the diffusion-weighted (DW) imaging characteristics of nonmalignant lesion subtypes assessed as false-positive findings at conventional breast magnetic resonance (MR) imaging. Materials and Methods: This HIPAA-compliant retrospective study had institutional review board approval, and the need for informed patient consent was waived. Lesions assessed as Breast Imaging Reporting and Data System category 4 or 5 at clinical dynamic contrast material-enhanced MR imaging that subsequently proved nonmalignant at biopsy were retrospectively reviewed. One hundred seventy-five nonmalignant breast lesions in 165 women were evaluated. Apparent diffusion coefficients (ADCs) from DW imaging (b = 0, 600 sec/mm(2)) were calculated for each lesion and were compared between subtypes and with an ADC threshold of 1.81 x 10(-3) mm(2)/sec (determined in a prior study to achieve 100% sensitivity). Results: Eighty-one (46%) lesions exhibited ADCs greater than the predetermined threshold. The most prevalent lesion subtypes with mean ADCs above the threshold were fibroadenoma ([1.94 +/- 0.38 {standard deviation}] x 10(-3) mm(2)/sec; n = 30), focal fibrosis ([1.84 +/- 0.48] x 10(-3) mm(2)/sec; n = 19), normal tissue ([1.81 +/- 0.47] x 10(-3) mm(2)/sec; n = 13), apocrine metaplasia ([2.01 +/- 0.38] x 10(-3) mm(2)/sec; n = 13), usual ductal hyperplasia ([1.83 +/- 0.49] x 10(-3) mm(2)/sec; n = 12), and inflammation ([1.95 +/- 0.46] x 10(-3) mm(2)/sec; n = 10). Atypical ductal hyperplasia ([1.48 +/- 0.36] x 10(-3) mm(2)/sec; n = 23) was the most common lesion subtype with ADC below the threshold. Lymph nodes exhibited the lowest mean ADC of all nonmalignant lesions ([1.28 +/- 0.23] x 10(-3) mm(2)/sec; n = 4). High-risk lesions (atypical ductal hyperplasia and lobular neoplasia) showed significantly lower ADCs than other benign lesions (P < .0001) and were the most common lesions with ADCs below the threshold. Conclusion: Assessing ADC along with dynamic contrast-enhanced MR imaging features may decrease the number of avoidable false-positive findings at breast MR imaging and reduce the number of preventable biopsies. The ability of DW imaging to help differentiate high-risk lesions requiring additional work-up from other nonmalignant subtypes may further improve patient care. (C) RSNA, 2012