Prospective Stage-Stratified Histopathologic Study and Proposed Disease-Evolution Model of Gluteal Permanent Synthetic Filler Complications

Participants will be enrolled before clinically indicated biopsy or filler-removal surgery. Exposure history, symptoms, physical findings, and MRI stage will be recorded using standardized forms. During surgery, samples from mapped tissue planes will be collected without extending the planned excision. Two pathologists blinded to clinical stage will independently grade eight tissue-injury domains and generate a composite severity score. Disagreements will undergo adjudication. The study will evaluate associations between tissue findings, time since injection, and clinical-radiologic stage and will use exploratory clustering to identify histopathologic phenotypes. Because participants are sampled at one operation, the resulting model will be described as a proposed cross-sectional natural-history framework.

Inclusion criteria

Age 18 years or older.

• Prior gluteal injection of a permanent or unknown nonresorbable filler.
• Clinically indicated biopsy or surgical excision yielding tissue suitable for histopathologic evaluation.
• Available history of approximate injection date and standardized preoperative clinical staging.
• Written consent for tissue analysis and optional future use of deidentified specimens.

Exclusion criteria

• Specimen composed only of scar or skin without tissue from the filler-affected region.
• Insufficient tissue quality for routine histology.
• Acute bacterial infection that precludes distinction of the underlying chronic tissue response unless infection is itself a prespecified advanced-stage feature.
• Prior oncologic radiation to the sampled gluteal region.
• Declined consent for research use of surgical tissue.