Breast MRI-detected cystic apocrine metaplasia: Imaging features with microvessel analysis and histologic correlation

OBJECTIVE. The purpose of this article is to characterize the histologic vascular features and distinguishing MR1 features of cystic apocrine metaplasia to better understand im-aging-pathology concordance. MATERIALS AND METHODS. Retrospective review of 261 consecutive MRl-guided biopsy cases was performed. Pathology results were reviewed for all biopsies; cystic apocrine metaplasia was identified as the predominant finding in 19 cases (7%). CD31 immunohisto-chemistry was subsequently performed on the most representative block of cystic apocrine metaplasia, and microvasculature was evaluated using computer-assisted image analysis. The contrast-enhanced MRI examinations correlating with the cystic apocrine metaplasia cases were independently reviewed by two radiologists specializing in breast imaging; lesions were analyzed for morphologic, kinetic, and T2 characteristics. RESULTS. On MRI review, 17 of 19 (89%) lesions were 10 mm or smaller. Washout kinetics were present in 11 of 19 (58%) lesions, and 14 of 19 (74%) lesions were at least partially hyperintense on T2-weighted sequences relative to adjacent glandular tissue. Cystic apocrine metaplasia had a higher percentage area (mean, 4.1%) of CD31-immunostained microvessels compared with background libroglandular tissue (mean, 1.2%). CONCLUSION. Cystic apocrine metaplasia should be considered in the differential diagnosis of a T2-hyperintense enhancing focus or subcenlimeter smoothly marginatcd mass, even if associated with washout kinetics. Cystic apocrine metaplasia contains a statistically significant increase in microvessel area compared with background libroglandular tissue and fat and, therefore, may be considered a concordant result for this set of imaging findings.