Epidural Effusion as Allergic Reaction Following Polyetheretherketone Cranioplasty: An Illustrative Case and Review of the Literature.

Well-described complications of polyetheretherketone (PEEK) cranioplasty in pediatric patients include surgical site infection, post-operative hematoma, cerebral edema, and implant fracture. We present a rare case of hypersensitivity to PEEK presenting as an epidural effusion in a 7-year-old male receiving a PEEK cranioplasty following a decompressive craniectomy. Within three weeks, the patient experienced fever and emesis. Erythrocyte sedimentation rate (ESR) was high (>130 mm/Hr) as well as C-reactive protein (CRP) (6.4 mg/dL). A brain MRI with contrast demonstrated both subgaleal and epidural fluid collections with T2 isointense columns projecting from the galeal surface, through the holes in the implant to the dural surface. The patient appeared clinically well. A sterile tap of the pericranial fluid showed no growth, b2-transferrin was negative, but the IgG level was high (>129.2 mg/dL) in the tap fluid. High-dose steroids reduced the epidural collection, but then the collection returned with steroid wean. A second cranioplasty operation replaced the PEEK flap with autologous bone. Postoperative imaging demonstrated markedly reduced fluid collections and a decreased midline shift. The patient remained clinically intact throughout the experience. PEEK allergy following cranioplasty is a rare entity and must be distinguished from infection or hematoma. Medical treatment with steroids can be attempted, but, if refractory, then appropriate treatment may necessitate removal of the offending PEEK implant.