Breast implant-associated late hematoma: a narrative review of case reports and case series.

Background and Objective: Late hematoma after breast implantation presents with delayed breast swelling or periprosthetic fluid that is clinically indistinguishable from breast implant-associated anaplastic large-cell lymphoma (BIA-ALCL), late seroma, infection, or tumor recurrence. This narrative review synthesized published case reports and small case series to describe clinical presentations, hypothesized mechanisms, diagnostic approaches, and management strategies. Methods: PubMed, Web of Science, and Cochrane Library were searched from inception to December 31, 2025. English-language case reports and case series documenting hematoma occurring ≥4 months after implantation were included. Two reviewers independently screened records and extracted data. Given the heterogeneity of uncontrolled case-level evidence, a qualitative descriptive synthesis was performed. Key Content and Findings: There were 37 articles involving 47 cases from 12 countries included. The median time from implantation to hematoma onset was 72.0 months. Patients typically presented with acute painful unilateral swelling. Features distinguishing late hematoma from BIA-ALCL included acute pain, absence of persistent effusion beyond 1 year, and magnetic resonance imaging (MRI) signal characteristics consistent with evolving blood products. Proposed mechanisms included capsular microfractures, chronic inflammation with neovascularization, external trauma, and iatrogenic factors such as anticoagulation. Ultrasound was the preferred initial screening tool; MRI provided definitive assessment of hematoma staging and implant integrity. Image-guided aspiration was essential to obtain fluid for cytology, microbiology, and CD30 immunohistochemistry to exclude BIA-ALCL. Surgical evacuation with capsulectomy was the most frequently reported definitive treatment; ultrasound-guided aspiration or arterial embolization were described in select patients with intact implants or poor surgical tolerance. Follow-up and recurrence data were inconsistently reported. Conclusions: Late hematoma should be considered in implant recipients with delayed swelling or periprosthetic fluid. Clinical evaluation, ultrasound, MRI, and image-guided aspiration guide management. Surgical evacuation with capsulectomy remains the primary reported treatment. These findings are descriptive only.