Mediastinal parathyroid adenoma detected by 99mTc-methoxyisobutylisonitrile: report of a case

We report herein the case of a 30-year-old man in whom ectopic mediastinal parathyroid adenoma was detected by 99mTc-methoxyisobutylisonitrile scintigraphy (99mTc-MIBI). The patient presented with a history of recurrent renal stones and was diagnosed as having primary hyperparathyroidism due to elevated serum levels of calcium and intact parathyroid hormone (i-PTH) levels. On admission, his serum calcium value was 12.1 mg/dl and the i-PTH level was 137 pg/ml. Ultrasonography, computed tomography (CT), and 201TlCl-99mTcO4- subtraction scintigraphy (Tl-Tc) were performed but none of these imaging techniques was able to detect an enlarged parathyroid gland. Selective venous sampling revealed that the serum i-PTH level was highest at 422 pg/ml in the left brachiocephalic vein. Exploration of the neck also proved unsuccessful. Finally, we performed 99mTc-MIBI which revealed and delineated an enlarged parathyroid gland in the upper mediastinum. Tumor extirpation was subsequently performed through a left thoracotomy. Pathologically, the tumor was confirmed to be a parathyroid adenoma and the serum calcium and i-PTH levels returned to within the normal ranges postoperatively.