Diffusion-Weighted MRI of Breast Lesions: A Five-Case Series Demonstrating Imaging Patterns and Diagnostic Pitfalls

Diffusion-weighted imaging (DWI) is an adjunct MRI sequence that helps characterize breast lesions by providing valuable information about tissue microstructure based on the in vivo motion of water molecules. Malignant lesions typically restrict the free diffusion of water molecules, appearing bright on high b-value images and dark (with a low apparent diffusion coefficient (ADC)) on the ADC map. Some benign lesions can show similar DWI findings, leading to diagnostic challenges when DWI is used as an independent sequence for lesion characterization. We report five breast MRI cases demonstrating varied diffusion patterns and the pitfalls encountered during interpretation. The cases include invasive ductal carcinoma with regional axillary nodal disease, metaplastic carcinoma, fibroadenoma without true diffusion restriction, fibroadenoma with true diffusion restriction, and a post-procedural seroma. Both malignant lesions showed restricted diffusion. Among the two pathologically proven fibroadenomas, one showed T2 shine-through, whereas the other demonstrated true diffusion restriction. The post-procedural lesion showed facilitated diffusion despite thin rim post-contrast enhancement, suggestive of a seroma. These cases demonstrate the overlap in diffusion findings between benign and malignant breast lesions, emphasizing the importance of interpreting diffusion images in conjunction with ADC maps, lesion morphology, enhancement patterns, and clinical history.