Parathyroid carcinoma presenting as a giant mediastinal retrotracheal functioning cyst

Parathyroid carcinoma is a rare malignancy of the parathyroid glands, and is the cause of primary hyperparathyroidism in fewer than one percent of cases. Symptoms are mainly due to local compression or hypercalcaemia secondary to markedly elevated parathyroid hormone levels. A minority of patients remain asymptomatic. Mediastinal parathyroid cysts are infrequent and may or may not be functioning. We present an 84-year-old woman with a giant functioning cystic parathyroid carcinoma located in the middle mediastinum. We performed a thorough MEDLINE and LILACS database search on published cases of parathyroid carcinoma and functioning parathyroid cysts, and found no case report with identical features to the one presented here.