MRI of the breast: comparison of MRI signals and histological characteristics of the same slices

The development of MRI with high spatial resolution and a special breast coil has contributed to more-accurate diagnosis of breast tumor, such as determination of morphologic characteristics including internal architecture of the breast lesion. To clarify how individual MRI findings reflect the pathological findings, we made slices of resected breast lesions identical to those obtained with axial MRI and compared them respectively according to histological subtype of tumors. In this article, we present MRI findings on the basis of histopathological evidence. In general, fibroadenomas (FA) show a well-defined border on contrast-enhanced fat-suppressed T₁-weighted images (CFT1). However, a subtype of fibroadenoma, mastopathic type, with a poorly defined border on CFT1 and carcinoma-like enhancement, is similar to cancer on MRI. Scirrhous carcinomas take either of two patterns on dynamic MRI, i.e., homogeneous enhancement or thick irregular peripheral ring enhancement. The latter type shows central fibrosis zones histologically. Papillotubular carcinoma shows a spotted pattern on dynamic MRI. The low-enhancement areas within the spotted pattern reflect parenchyma between clusters of cancer. Solid-tubular carcinoma shows thin peripheral enhancement on dynamic MRI and linear high signal on CFT1. This finding of CFT1 corresponds to infiltration of lymph cells and fibroblast cells in the adjacent zone. Invasive lobular carcinoma shows nonmass lesions and a slow gradual enhancement pattern. Mucinous carcinomas show high signal intensity on T₂-weighted images because of mucin and reveal gradual enhancement. The ill-defined border of mucinous carcinoma on CFT1 is useful to distinguish it from FA.