Pseudoangiomatous hyperplasia of mammary stroma: a case of pure type after removal of fibroadenoma.

A case of pure pseudoangiomatous hyperplasia of the mammary stroma after removal of a fibroadenoma is described. The lesion, which was found in the right breast of a 40-year-old woman, was a well-circumscribed non-encapsulated, rubbery, lobulated mass measuring 40x40x35 mm. Histologically, it consisted predominantly of a proliferation of spindle cells with interanastomosing vascular-like arrangements in the interlobular or interductal stroma. Neither cytological atypia nor mitotic figures were observed. The stroma contained abundant collagen with focal hyalinization. Focally, epithelial elements showed mild ductal hyperplasia. There was no fibroadenoma. Immunohistochemically, the spindle cells were positive for vimentin, CD34, alpha-smooth muscle actin, muscle actin, CD34, calponin, and progesterone receptors. Ultrastructurally, many spindle cells had thin elongated cytoplasmic processes, which enveloped pseudovascular spaces containing a few collagenous fibrils, indicating fibroblastic cells. This lesion should be distinguished from other mammary fibrous and vascular lesions with which it may be confused.