Incidentally discovered severe hypercalcaemia from a functioning parathyroid cyst: the limitations of intraoperative parathyroid hormone (IOPTH) monitoring.

Parathyroid cysts (PCs) are rare pathologies and are typically non-functional (do not secrete parathyroid hormone (PTH)). The aetiology of PCs is highly debated, and management is complex. We present a unique case of a parathyroid adenoma contained within a functional PC and highlight the limitations of intraoperative PTH monitoring during the surgical resection of functional PCs.