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Background
Most breast disorders of pregnancy and lactation are benign, but pregnancy-associated breast cancer is not uncommon, accounting for 3% of all breast malignancies. Physiologic changes in pregnancy and lactation cause dramatic changes in breast tissue composition, decreasing the sensitivity of mammography for detecting breast cancer. It is of utmost importance that radiologists understand physiologic changes and common breast pathologies in pregnancy and lactation to avoid delayed diagnosis.

Educational Goals / Teaching Points
Be familiar with the American College of Radiology (ACR) appropriateness criteria for mammography, ultrasound, and MRI in pregnancy and lactation. Recognize and describe the physiologic changes of the breast during pregnancy and lactation. Understand the pathology and radiographic features of infectious and inflammatory conditions and benign breast lesions in pregnancy and lactation. Recognize the radiographic features and understand the pathology and management of pregnancy-associated breast carcinomas (PBAC).

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
During pregnancy, breast parenchyma undergoes marked ductal and lobular growth. Lactation causes distension of the lobular glands and accumulation of milk products. These changes result in markedly increased breast density. Gestational or secretory hyperplasia can cause microcalcifications, closely resembling malignancy. Puerperal mastitis occurs most often during breastfeeding. The most common organism is Staphylococcus aureus. Sonography will show trabecular thickening due to edema. Puerperal abscesses will appear as an irregular, hypoechoic, or anechoic mass with internal debris. Galactoceles are caused by the stagnation of milk products in ducts, typically after the cessation of breastfeeding. Their appearance can be variable depending on the fluid, fat, and protein. They can appear as a cystic mass with a fat-fluid level, pseudolipoma, or pseudo-hamartoma. Lactating adenomas are characterized by lobules of secretory hyperplasia separated by connective tissue. They can spontaneously regress after lactation. Radiographically, lactating adenomas are indistinguishable from fibroadenomas. PBAC is defined as breast cancer occurring during pregnancy or within 1 year of delivery. Patients often present with a palpable mass and tend to have more advanced disease at diagnosis. Hormone-receptor-negative and HER2/neu-positive tumors are associated with aggressive growth patterns.

Conclusion
PBACs are primarily the same as those in nonpregnant women. However, physiologic changes in pregnancy and lactation present a unique diagnostic challenge to the radiologist. Knowledge of these changes and unique entities associated with pregnancy and lactation can help the radiologist make a timely diagnosis and improve patient outcomes.