Normal and pathologic tissue reactions to soft tissue gel fillers.

Background: All gels act as foreign bodies. Host response ranges from a few macrophages to an intense foreign-body reaction with fibrosis, depending on gel type. For polymer gels the filling effect stems from their volume. For combination gels it stems from the intended host foreign-body reaction to the microparticles.

Objective: This review explains how host tissue reacts with different gel types and how adverse reactions differ depending on gel type.

Methods: This study is based on observations during the past 6 1/2 years from experimental/clinical studies and biopsies from adverse reactions.

Results: Hydrophilic polymer gels constantly exchange water with their host tissue with minimal fibrosis. Degradable gels are encircled and degraded by macrophages; polyacrylamide gel is traversed by macrophages, replaced by fibrous, vessel-bearing strands. All other gels provoke a foreign-body reaction with ensuing fibrosis. Adverse reactions include bacterial infection for the hydrophilic gels and a fibrous granuloma for all other gel types. It is hypothesized that bacteria are maintained within a biofilm (a film comprising bacteria, their nutrients, and their waste products) giving rise to a low-grade infection.

Conclusions: Infectious nodules must be treated with antibiotics. Granulomas must be treated with a combination of both steroids and antibiotics or excision.