Pseudoaneurysmal bone cyst secondary to primary hyperparathyroidism mimicking early infection following hip arthroplasty: A case report.

Pseudoaneurysmal bone cysts are rare complications of advanced primary hyperparathyroidism, mimicking malignant lesions or postoperative infections, particularly when accompanied by wound drainage and elevated inflammatory markers. A 49-year-old man underwent cemented total hip arthroplasty for a pathological femoral neck fracture. Persistent postoperative bloody-serous discharge and elevated infection markers such as C-reactive protein suggested early periprosthetic joint infection, prompting two surgical revisions. During both revision procedures, multiple deep tissue samples were obtained and sent for aerobic and anaerobic cultures with extended incubation as well as histopathological analysis. All microbiological cultures remained negative. Histopathology revealed a giant cell-rich, hemorrhagic, fibrous lesion consistent with a pseudoaneurysmal bone cyst due to undiagnosed primary hyperparathyroidism. Timely surgical debridement, microbiological sampling, and empiric antibiotics ensured patient safety while the metabolic etiology was being established. Biochemical tests confirmed hypercalcemia and elevated parathyroid hormone from a parathyroid adenoma. Primary hyperparathyroidism-induced osteoclastic activity can produce hemorrhagic cystic lesions resembling infection or malignancy. Meticulous surgical exploration, repeated microbiological sampling, and histopathological analysis excluded infection and malignancy, while definitive management via parathyroidectomy prevents further skeletal complications. This case emphasizes structured diagnostics and interdisciplinary orthopedic-endocrine collaboration for managing rare primary hyperparathyroidism complications effectively and underlines that persistent postoperative drainage with repeatedly negative cultures should prompt metabolic evaluation.