Robust foreign body giant cell reaction after polymethyl methacrylate cranioplasty: illustrative case

BACKGROUND: Foreign body giant cell reaction to a cranioplasty implant is a rare complication of this common neurosurgical procedure, and it may cause clinically significant symptoms. Here, the presentation, imaging, management, and pathology of a patient who developed a robust fibroinflammatory reaction to a polymethyl methacrylate (PMMA) cranioplasty implant are reviewed to aid with future timely diagnosis and management of this complication. OBSERVATIONS: A 38-year-old male who previously underwent decompressive craniectomy after a gunshot wound to the head with subsequent PMMA cranioplasty presented 1 month postoperatively with surgical site swelling and fevers. MRI demonstrated a subgaleal fluid collection and an epidural mass. The patient was initially treated empirically with antibiotics but remained febrile and developed worsening headache. The patient underwent surgical removal of the implant with excision of fibrovascular tissue after interval MRI demonstrated enlargement of the epidural mass. Intraoperative cultures were negative, and pathological evaluation confirmed the diagnosis of fibrovascular granulation tissue with foreign body giant cell reaction. Postoperatively, the patient's symptoms resolved. LESSONS: Fibroinflammatory reactions to synthetic cranioplasty materials can mimic surgical site infections, but key imaging, laboratory, and clinical findings can support the diagnosis. Timely treatment with surgical removal of the implant may be curative. https://thejns.org/doi/10.3171/CASE26817.