Natural History of Injectable Permanent Synthetic Filler Disease

Inclusion Criteria: * Adults with a documented history of injection of permanent synthetic or modeling substances into the gluteal region. Available date or sufficiently reliable estimated date of filler injection to determine disease duration. Prospective clinical assessment documenting local and/or systemic manifestations. Available magnetic resonance imaging of the affected anatomical region performed as part of clinical evaluation. Clinically indicated surgical removal of affected tissue. Histopathologic tissue specimen available and of sufficient quality for standardized review. Availability of the core clinical, radiologic, and histopathologic variables required for the primary analysis. Written informed consent when required by the approved research protocol. Exclusion Criteria: * Exposure exclusively to temporary or resorbable fillers without evidence of permanent synthetic filler exposure. Inability to determine the approximate date of filler injection. Histopathologic specimens insufficient for standardized evaluation. Magnetic resonance imaging unavailable or technically inadequate for assessment of disease distribution. Incomplete core clinical data preventing evaluation of the prespecified study outcomes. Previous complete surgical removal of the injected material before the index clinical and imaging assessment, when this prevents reconstruction of the untreated disease state.