Complex Cystic and Solid Masses

Imaging Findings Complex cystic and solid masses (CCSMs) contain both cystic and solid elements that may manifest sonographically as predominantly cystic lesions with solid mural nodule(s) or thick irregular walls, thick septations with or without perceptible internal vascularity, or be predominantly solid with a minor cystic component. CCSMs can usually be distinguished from complicated cysts or clustered cysts by ultrasound. On mammography and tomosynthesis, CCSMs are frequently indistinguishable from entirely cystic or entirely solid masses, and may have varying density, ranging from hypo- to hyperdense, and with margins ranging from circumscribed to irregular. Both malignant and benign lesions can present as CCSMs and these can be palpable or screening detected and occur in patients of all ages and genders. Pathology Findings The vast majority of cystic lesions in the breast are benign and include reactive lesions, inflammatory lesions, and benign papillary tumors. Breast cysts are seen predominantly in perimenopausal women. Aspiration of cysts that are bloody are subjected to cytologic evaluation. Complex cystic lesions result from accumulation of proteinaceous debris with foamy macrophages, apocrine cells, blood elements or crystalline structures. When reviewing core needle biopsy of cystic and solid masses, the wall of the cyst with lining epithelium may be visualized at the edge or periphery of the core. Papillary apocrine metaplasia usually corresponds to the solid component of the cyst. Similarly, histiocytes and inflammation in the cyst lining or surrounding breast tissue may be related to duct ectasia or leakage of cyst contents. Presence of calcifications, cholesterol clefts, and foreign body giant cells are indicative of fat necrosis. Cystic papillomas present with nipple discharge. Cystic lesions during pregnancy and lactation may be due to a galactocele or abscess. Malignant cystic lesions are rare but can be seen in papillary carcinoma and poorly differentiated ductal carcinomas particularly in apocrine carcinomas which can present as cystic and solid masses.