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Galactocele is essentially a retention cyst resulting from the obstruction of a lactiferous duct, usually by a protein plug. It typically presents as a painless breast mass in young lactating females. The lesions may be single or multiple and unilateral or bilateral.

Mammography: They appear as circumscribed lesions with hypodense upper area (containing lighter lipid components of the cyst contents) and a lower area (with water-based components) that is isodense with the surrounding tissue. The interface between the two zones tends to remain horizontal as the patient changes position.

Cytology: The diagnosis can be made by fine needle aspiration. The cyst content resembles milk and contains necrotic cells, nuclear debris, and a few inflammatory cells. Biochemical analysis will show proteins, fats, and lactose. The contents of long-standing lesions may be viscous and appear yellow or brown in color. When secondarily infected, the cyst fluid has pus-like appearance and contains abundant neutrophils.

Gross & Microscopic: Grossly, the cyst wall may be lined by inspissated cheese-like caseous material. Microscopically, they are lined by cuboidal or flat epithelium with vacuolated cytoplasm due to lipid accumulation. The cyst wall may be surrounded by a zone of fibrosis. If the cyst contents leak into the surrounding tissues, it may invite chronic inflammatory reaction and even secondary infection. The treatment in most cases consists of aspiration of the cyst contents; some patients undergo excisional biopsy.