Pathological Features of Breast Fibroadenoma
On gross examination, fibroadenomas are clearly demarcated from surrounding breast tissue, mobile, firm in texture, and smooth on the surface. Tumors are usually round or oval, often covered by a thin, intact fibrous capsule. When fibrous components dominate, the cut surface appears gray-white, semi-transparent, firm, and elastic. When epithelial components are abundant, the cut surface appears pale pink, granular, sometimes papillary, protruding outward, and softer in texture.
Under light microscopy, based on the extent of fibrous and epithelial component growth and their structural relationship, fibroadenomas are classified into three pathological types: intraductal, periductal, and mixed.
(1) Intraductal type: Hyperplastic fibrous tissue compresses ducts, causing elongation, bending, and deformation. In severe cases, interstitial components appear to invade the duct lumen. The ductal epithelium becomes flattened due to compression. The fibrous tissue is relatively loose, sometimes mucoid.
(2) Periductal type: Epithelial and fibrous components are intermixed. Ducts appear round, oval, or irregular, not compressed by hyperplastic fibrous tissue. The duct lumen consists of two layers of epithelial cells: inner layer composed of cuboidal or columnar epithelium, outer layer consisting of myoepithelial cells with clear cytoplasm. Mild epithelial hyperplasia may occur. Fibrous tissue is hyperplastic and surrounds the ducts, being loose or dense, occasionally showing collagen degeneration.
(3) Mixed type: Features of both intraductal and periductal types are present simultaneously.
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