Histological and immunohistochemical characteristics of capsular synovial metaplasias that form around silicone breast implants

Metaplasia is a reversible phenomenon that usually occurs in response to chronic irritation and/or inflammation. It allows for the substitution of fragile cells with those that are better able to survive under various circumstances. Our study aims to describe the histology of one unusual type of metaplasia results in the formation of a synovial-like membrane typical of joints inside a female patient’s breasts around silicone implants. We analyzed samples from 22 female patients, who underwent delayed-staged breast reconstructions. Attention was paid especially to tissue that was in direct contact with the silicone expander and that was under permanent pressure and friction between the implant and the surrounding tissue. Biopsies of explanted periprosthetic capsules were processed for examination by light microscopy. Immunohistochemical staining (ten different primary antibodies) was performed to examine a variety of cell-specific antigens. At the interface between the tissue capsule and the silicone breast expander, we typically observed a 50–200-μm cellular lining. Thanks to the high cellular density, this cellular layer resembled epithelium. However, there was no basement membrane, and cells were negative for cytokeratin. The cells forming the superficial layer were strongly positive for vimentin and podoplanin and weakly positive for the S100 protein. These cells did not express desmin or smooth muscle actin. Within the most superficial layer (synovial intima), we distinguished two types of cells: phagocytic (CD68-positive) and fibroblast-like synovial cells. We conclude that the cellular lining surrounding silicone breast implants looks like a true synovial membrane resembling a fibrous form of synovium.