Histological assessment of fifty breast capsules from smooth and textured augmentation and reconstruction mammoplasty prostheses with emphasis on the role of synovial metaplasia.

: Fifty breast capsules surrounding smooth and textured breast prostheses were reviewed histologically, immunohistochemically, and ultrastructurally, and findings correlated with patient data. The histology of the capsules varied; although most consisted of a simple fibrocollagenous membrane, some were lined by organized, round to polyhedral cells similar to synovium. Histologically, the lining of the synovial type consisted of epithelioid cells overlying parallel bands of collagen, with basally located nuclei and cytoplasmic processes directed toward the surface and arranged within a well developed reticulin network. Immunohistochemically, the cells were vimentin positive, weakly positive focally for alpha-1-antitrypsin, alpha-antichymotrypsin, and lysozyme, and negative for EMA and AE1/AE3. Scanning electron photomicrographs showed a bosselated luminal lining overlying parallel bands of collagen. By transmission electron microscopy, both secretory and phagocytic cells could be distinguished. Some of the former were multinucleated. No basement membrane material could be identified, and cell junctions were rare. Histologically, immunohistochemically, and ultrastructurally the lining appeared identical to synovium and to the synovial metaplasia that has been described in sutured skin, after repeated subcutaneous injections of air, the bone-cement interface of loose hip prostheses and adjacent to gliding silastic tendon reconstruction rods. The physical and chemical composition of the prostheses, the mechanical forces, and the developmental response of the host mesenchymal tissue are thought to influence the formation and maintenance of the synovial metaplasia of the breast capsule.