Hyperparathyroidism due to a cystic parathyroid adenoma after irradiation of the neck

A 48-year-old female with hypercalcaemia diagnosed 3 years prior to admission is described. The patient underwent x-ray therapy of the neck for keloid scars 35 years prior to the diagnosis of hypercalcaemia. The hypercalcaemia was found to be the result of primary hyperparathyroidism. A cystic parathyroid adenoma was identified during surgery and was, on microscopic examination, composed of oxyphil cells rich in mitochondria. The cystic fluid contained 360 times higher C-terminal PTH than peripheral serum and almost 4000 times higher PTH as intact 1-84 amino acid residue species. We concluded that previous X-ray irradiation was related to the pathogenesis of the patient's parathyroid adenoma. The mild nature of the patient's hyperparathyroidism was possibly related to the composition of the tumour of oxyphil cells, known to be a poorly functioning variant of the parathyroid cell. Since parathyroid 'cysts' are obviously necrotic parathyroid adenomas, aspiration of the cysts alone cannot be expected to be curative and, therefore, it is recommended to treat cystic parathyroid adenomas by surgical extirpation.