Background enhancement of mammary glandular tissue on breast dynamic MRI: imaging features and effect on assessment of breast cancer extent

Just as mammographic breast density influences mammographic sensitivity, the degree of background enhancement in breast magnetic resonance imaging (MRI) may influence the sensitivity of breast MRI. The purpose of this study is to assess the influence of background enhancement on the accuracy of breast cancer extent assessment using MRI and to assess the correlation between the accuracy of breast cancer extent assessment and the kinetic analysis of background enhancement in dynamic contrast-enhanced MRI. Seventy bilateral breast MRI examinations were evaluated to assess the extent of a known primary tumor. Background enhancement was classified into four categories by visual assessment: minimal, mild, moderate, and marked, in the early dynamic phase and in the late dynamic phase. The correlation of the results with histological findings was examined. Background enhancement grade showed a significant tendency to increase during dynamic contrast-enhanced MRI. When classifying background enhancement at early dynamic phase, the accuracy of tumor extent assessment by MRI with moderate/marked background enhancement was 60%, which was lower than the 78% accuracy with minimal/mild background enhancement, but not significantly so (p = 0.153). When classifying background enhancement at late dynamic phase, the accuracy with moderate/marked background enhancement was 61%, which was significantly lower than the 83% accuracy with minimal/mild background enhancement (p = 0.034). There was no tumor-size-related bias between the groups (p = 0.089). The degree of background enhancement on breast MRI affects the accuracy of breast cancer extent assessment, especially at late dynamic phase.