Clinical and Imaging Features Associated With Malignant Focal Nonmass Enhancement on Breast MRI.

Introduction: Focal non-mass enhancement (NME) is a common breast MRI finding with limited data to guide management. This study aimed to assess clinical and imaging features of malignant BI-RADS 4 focal NME.

Methods: This IRB-approved, retrospective study included breast MRI exams between August 1, 2013 and September 1, 2022 yielding BI-RADS 4 focal NME lesions that underwent core biopsy or excision with available pathology result or demonstrated decrease or resolution during follow-up MRI or at least 2 years of MRI stability.

Results: A total of 296 BI-RADS 4 focal NME lesions in 246 patients were included in the study. The overall malignancy rate of BI-RADS 4 focal NME was 36/296 (12.2%). Focal NME in a patient presenting for evaluation of extent of disease or other diagnostic concern was 5.5 and 3.4 times more likely, respectively, to be malignant compared to focal NME seen on a high-risk screening exam. There was also a significant association between malignancy and focal NME that was brighter than background parenchymal enhancement (BPE) on maximum intensity projection (MIP) images. There was no significant association between malignancy and lesion size, internal enhancement pattern, amount of BPE, amount of fibroglandular tissue, or signal intensity on T2-weighted images.

Conclusion: Our study yielded a malignancy rate of 12.2% for BI-RADS 4 focal NME lesions. Indication for MRI and signal intensity compared to BPE on MIP images were features associated with malignancy that may provide guidance on the management for focal NME.