Brown tumor mimicking giant cell tumor in primary hyperparathyroidism: a case report.

Background: Differentiating brown tumor due to primary hyperparathyroidism from a giant cell tumor remains a clinical challenge. Misdiagnosis may lead to inappropriate oncologic treatment and unnecessary surgical interventions.

Case presentation: We report the case of a 52-year-old Caucasian white woman of Albanian ethnicity with multiple osteolytic bone lesions and a history of repeated orthopedic surgeries over 5 years. Initial histopathology suggested aneurysmal bone cyst and giant cell tumor, while imaging findings were interpreted as metastatic bone disease, and led to chemotherapy and radiotherapy in the absence of a confirmed primary malignancy. The patient was later referred to our Nuclear Medicine Unit, where a repeat bone scintigraphy indicated metabolic bone disease. A full biochemical evaluation revealed severe hypercalcemia and elevated parathyroid hormone. Parathyroid scintigraphy confirmed a hyperfunctioning parathyroid adenoma. Retrospective review of previous pathology reports supported the diagnosis of brown tumor. The patient underwent successful parathyroidectomy. Biochemical parameters normalized within 3 months postoperatively, and no complications such as hypocalcemia were observed.

Conclusion: This case illustrates the importance of early consideration of primary hyperparathyroidism in the differential diagnosis of multifocal lytic bone lesions. Accurate diagnosis requires a multidisciplinary approach combining imaging, histopathology, and biochemical evaluation to prevent misdiagnosis and overtreatment.