Capsular synovial metaplasia mimicking radiographic features of implant-associated anaplastic lymphoma

Delayed onset breast implant-associated reactions range widely in symptomatology and underlying etiology. With increasing reports of breast implant-associated anaplastic large cell lymphoma (BIA-ALCL), findings such as unilateral breast swelling, capsular thickening, and peri-implant fluid raise concern. Synovial metaplasia is a benign histologic finding commonly associated with implant capsules and can be an unusual cause of such symptoms. Though the clinical significance of synovial metaplasia is unknown, it is important to consider this entity in the differential diagnosis for delayed onset breast symptoms, with signs otherwise concerning for BIA-ALCL or infection.