A rare case of a parathyroid adenoma inside a parathyroid cyst.

Parathyroid cysts (PCs) are rare lesions, located in the neck and anterior mediastinal region. The vast majority are non-functioning, presented as nodular cervical lesions. Large, non-functioning PCs can manifest with compressive symptoms of the surrounding tissues. Rarely, PCs produce excessive amounts of parathyroid hormone (PTH), resulting in primary hyperparathyroidism. We report a case of functional PC, describing its diagnostic and therapeutic approach.