Parathyroid cysts are rare. When they do occur they usually have no demonstrable endocrine function, but may cause respiratory distress by tracheal compression or may be mistakenly diagnosed as thyroid carcinomas or adenomas. We report a case of a parathyroid cyst which presented with hypercalcemia. CASE REPORT: A fifty eight year old man undergoing routine investigations was found to have hypercalcaemia. His calcium level was elevated to 3.63 mmol/l and the serum parathyroid hormone level was 18.4 pmol/l (normal range 1.0- 5.3). Serum alkaline phosphatase was at the upper limit of normal at 1 1 3U/1. X-ray of the renal tract revealed no evidence of calcification. He was asymptomatic and had no palpable neck mass. Ultrasound examination revealed a 3 cm cyst-like structure inferior and posterior to the left lobe of the thyroid, with a well defined wall approximately 2 mm thick. Exploration of the neck revealed a large cyst (6.5 x 5 x 3 cm), which was removed and found to weigh 57 g. Three other parathyroid glands with a normal appearance were found. Macroscopic examination of the removed specimen showed a smooth lined cyst containing greasy, pearly material. Histology revealed a fibrous lined cyst, containing several islands of parathyroid tissue with clear cell cytology and moderate nuclear pleomorphism. Post-operatively serum calcium returned to normal. The patient was discharged on the fourth post-operative day. DISCUSSION Many theories have been advanced regarding the aetiology of parathyroid cysts. Goris1 was the first to report a case. Nylander2 has suggested that they arise from remnants of the third or fourth pharangeal pouch or are vestigia
