Genuine granuloma formation following implantation of injectable dermal fillers is a rare complication, with incidences ranging from one in 100 patients (1 percent) to one in 5000 (0.02 percent). Foreign body granulomas occur several months to years after injection at all implantation sites at the same time. Without treatment, they may grow to the size of beans, remain virtually unchanged for some years, and then resolve spontaneously. Three clinical and histologic types of foreign body granulomas can be distinguished:
- Cystic granulomas (synonyms: inflammatory, palisading, collagenolytic): these are caused mainly by injected biological gels such as collagens and hyaluronic acids. Their clinical signs are fluctuation (sterile abscess), extreme redness, and induration. Cystic granulomas are small and superficial, occur within the first year, and disappear spontaneously within another year. They are surrounded by a significant number of giant cells.
- Edematous granulomas (synonym: lipogranuloma): these are caused by artificial fluids such as silicone and polyacrylamides. They appear suddenly years after injection with extensive swelling and are surrounded and infiltrated by mononuclear and inflammatory cells.
- Sclerosing granulomas (synonyms: sarcoidal and xanthelasmic): these are caused by particulate injectables composed of polymethylmethacrylate, polylactic acid, poly-hydroxyethyl-methacrylate, calcium-hydroxylapatite, or dextran microspheres. Sclerosing granulomas occur generally 6 months to 3 years after implantation and are visible, often bluish confined nodules. Histologically, the implant is infiltrated by many macrophages and giant cells, fibroblasts, and collagen fibers but few inflammatory cells.
Permanent implants are not characterized by a higher rate of foreign body granuloma per se than temporary implants; however, their clinical appearance is more pronounced and their persistence longer if not treated adequately.