PRIMARY HYPERPARATHYROIDISM INDUCED BY AN ECTOPIC ADENOMA, INITIALLY PRESENTED AS BROWN TUMOR OF THE TIBIA

Abstract

The classic manifestation of unchecked, advanced hyperparathyroidism is the brown tumor, a non-neoplastic giant cell osteomedullary lesion. We report a case of, these days rarely seen manifestation of advanced hyperparathyroidism, brown tumor due to an ectopic mediastinal parathyroid adenoma. A 63-years-old woman presented with an expansile osteolytic lesion of the right tibia on the radiographic images. Because of the suspicion of primary or secondary bone tumor, bone scintigraphy was performed. The bone scan was indicative of metabolic bone disease. Furthermore, laboratory investigations were obtained that revealed hypercalcemia, hypophosphatemia, increased level of alkaline phosphatase, and parathyroid hormone. Subsequently, ultrasound of the neck was performed, but no enlarged parathyroid glands were detected, so the patient underwent dual-phase 99mTc-methoxy-isobu- tyl-isonitrile (MIBI) parathyroid scintigraphy using a hybrid SPECT/CT gamma camera. The MIBI scan showed ectopic hypermetabolic parathyroid tissue in the anterior mediastinum, as well as an additional appearance of focal radiotracer uptake in the sternal end of the right clav- icle, suggesting the presence of a brown tumor. After thorough clinical workup, the diagnosis was in favor of primary hyperparathyroidism and the patient underwent surgical resection of the ectopic parathyroid gland with gamma-probe guidance, later histopathologically confirmed it to be a parathyroid adenoma. Postoperatively her PTH level dropped and the electrolyte status normalized within 6 months. Osteolytic brown tumors can easily imitate bone malignancy and should be evaluated with caution. The use of intraoperative gamma-probe guidance could support the complete removal of the parathyroid adenoma tissue ensuring the surgical and therapeutic success for the patient.