Natural History of Injectable Permanent Synthetic Filler Disease

Injectable permanent synthetic filler disease is characterized by heterogeneous local and systemic manifestations that may emerge years after filler injection. Although inflammatory reactions, migration, foreign-body granulomas, adipose tissue injury, fat necrosis, and fibrosis have been individually described, the temporal clinicopathologic evolution of the disease remains poorly characterized. This prospective observational cohort study aims to characterize the natural history of disease associated with injectable permanent synthetic fillers by integrating time since injection, clinical manifestations, magnetic resonance imaging findings, and histopathologic tissue features. Participants with a history of gluteal injection of permanent synthetic fillers who undergo clinical evaluation, magnetic resonance imaging, and clinically indicated surgical removal of affected tissue will be evaluated. Histopathologic findings will be systematically assessed for adipose tissue injury, acute and chronic inflammation, foreign-body granulomatous reaction, fat necrosis, fibrosis, characteristics of the exogenous material, and vascular or lymphatic involvement. The primary objective is to determine how histopathologic disease patterns vary according to time since injection. Secondary objectives include evaluating temporal associations with clinical symptoms, extent of migration on magnetic resonance imaging, fibrosis, granulomatous inflammation, and evidence of superimposed inflammatory reactivation.

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.