THE SYNOVIAL STRUCTURE OF BREAST-IMPLANT-ASSOCIATED BURSAE

Over 2 million silicone breast prostheses have been implanted since th ey were introduced in the 1960s. After implantation, a fibrovascular t issue reaction referred to as a ''capsule'' is observed. Many consider this capsule to be a static structure, an effective barrier to the eg ress of foreign material. However, reports documenting the presence of silicone within lymph nodes of patients with apparently unruptured im plants indicate that silicone may be transported away from the breast- implant capsule. To characterize the cells making up the breast-implan t capsule, 183 capsules from 103 ruptured or bleeding implants and 80 intact implants were studied. Gross and light microscopic studies were performed on all, and selected capsules were subjected to ultrastruct ural study and Fourier-transform infrared spectroscopy. Light microsco pic examination of the capsule revealed an organized, layered structur e with an associated network of endothelia-lined spaces. The capsules varied in cellularity, depending on the type and integrity of the impl ant. The superficial cell layer of all capsules had cytoplasmic proces ses directed toward the surface. These long cytoplasmic processes cont ained vacuoles ultrastructurally, indicating phagocytic and pinocytoti c capability. These cells bore immunological markers of bone marrow de rived macrophage-type cells. The extracellular matrix of the surface l ayer consisted of an amorphous fibrillar protein lacking the ultrastru ctural periodicity of mature collagen. No cell-to-cell junctions were observed. Deeper capsular layers were characterized by fibroblast-type cells in a collagen matrix. No capsules studied contained basement me mbrane or basal lamina between the stroma of the capsule and the surfa ce cells. The absence of cell junctions and basement membrane or basal lamina indicates that phagocytic cells from the surface have free acc ess to capillary networks in deeper tissues. FTIR Fourier-transform in frared spectroscopy confirmed the presence of silicone in histiocytes lining the capsule space, dispersed between layers of mature collagen, in perivascular aggregates, and deep to the collagen layers of the ca psule. The structure of breast-implant-related capsules is identical t o the synovial structure of bursae and joints; therefore, it is likely that the breast-implant-associated capsule functions like synovium an d participates in the movement of particles from the capsular surface to deeper structures.