A parathyroid adenoma masquerading as an oesophageal cyst.

A male in his 60s presented with ventricular fibrillation arrest, severe hypercalcaemia and elevated parathyroid hormone levels. A diagnosis of primary hyperparathyroidism (PHPT) was suspected. Initial imaging, including single-photon emission CT, failed to localise the suspected parathyroid adenoma (PTA). Further imaging review revealed a mediastinal cystic mass adjacent to the oesophagus. Thoracic surgery consultation was undertaken and it was felt the cyst was an unrelated duplication cyst. The patient continued to have uncontrolled calcium levels and therefore an exploratory parathyroidectomy was performed. Postoperative pathology confirmed the oesophageal cyst was a PTA. These cysts are associated with more severe clinical manifestations and higher calcium, likely due to delayed diagnosis and localisation. This case underscores the importance of using multiple imaging modalities for preoperative localisation, especially in atypical cases of PHPT. Mediastinal PTA, despite its extreme rarity, should be considered with incidental PHPT and a seemingly extraneous mediastinal mass.