Background: Breast MR imaging has emerged as a highly sensitive modality for the imaging of breast tumors. However, a standardized method of interpretation of lesions showing non-mass-like enhancement does not exist. The purpose of this study was to analyze the features of non-mass-like breast lesions detected by MRI, and to establish a standardized method of interpretation to allow categorization of these lesions.
Methods: A retrospective review was performed for 102 consecutive nonpalpable mammographically occult, non-mass-like lesions detected by MRI that had undergone ultrasound-guided vacuum-assisted biopsy. MR imaging was performed on a 1.5-Tesla system. The distribution patterns were classified into three categories as follows: single quadrant/solitary lesion (linear), single quadrant/grouped lesion (focal, regional, segmental), and multiquadrant lesion (multiple regions, diffuse). The presence of a ductal pattern was assessed in the enhancing lesions after the tumor distribution had been decided. In addition to the BI-RADS-MRI descriptors, the presence of clustered ring enhancement was also assessed in heterogeneous enhancing lesions. We divided non-mass-like lesions into those with a small (category 3a), moderate (category 3b), or substantial (category 4) likelihood of malignancy.
Results: The features with the highest positive predictive value (PPV) for cancer were clustered ring enhancement (67%) (P = 0.004), a branching-ductal pattern (38%) (P = 0.003), and clumped architecture (20%). The PPV for cancer of a linear-ductal pattern was 11% (1/9). All lesions showing multiquadrant distribution, linear-nonspecific lesion, non-branching pattern with homogeneous and stippled internal architectures, and heterogeneous lesion without clustered ring enhancement were diagnosed as benign.
Conclusion: Non-mass-like breast lesions detected on MRI showing a clustered ring enhancement, a branching-ductal pattern, and clumped architecture should be evaluated further by biopsy (category 4), while lesions not showing these characteristics may be observed without unnecessary intervention (category 3a). Lesions showing a linear-ductal pattern may be followed carefully or evaluated by biopsy as needed (category 3b).