We present two patients with an unusual cause of primary hyperparathyroidism.
A 50 year old man was referred due to incidentally noted raised serum calcium consistent with primary hyperparathyroidism (adjusted calcium 3.52 mmol/L, phosphate 0.66 mmol/L, PTH (parathyroid hormone) 99.5 pmol/L, Vitamin D 46 nmol/L). An initial neck ultrasound demonstrated a 1.2x1.7 cm left sided presumed parathyroid nodule but also a cystic 3.3x3.2x1.7 cm right sided mass. Isotope MIBI scan was negative. Due to the significantly raised serum calcium, the left sided nodule was excised. However post-operatively, the calcium remained significantly raised requiring inpatient admissions for rehydration. On follow up, fluid from the cyst was aspirated and sent for PTH analysis; PTH was >200 pmol/L. Following surgical removal, the hyperparathyroidism has been cured with histology consistent with a parathyroid adenoma with cystic degeneration.
A 73 year old man had incidentally detected hypercalcaemia by his GP. Investigations revealed adjusted calcium 2.79 mmol/L, PTH 30.0 pmol/L, vitamin D 28 nmol/L, phosphate 0.50 mmol/L. A neck ultrasound showed a 3.5x4.4 cm cystic mass; No solid adenoma was identified. An isotope MIBI scan and 4D CT were negative. His calcium was monitored however it rose to 2.89-3.19 mmol/L despite adequate hydration. Cyst fluid aspirate showed PTH levels >200 pmol/L. He is currently awaiting surgical removal of the parathyroid cyst.
Parathyroid cysts were first described in 1880 and since then, around 300 cases have been described in the literature. They are rare occurrence, with 0.5-1% of all parathyroid lesions being cysts and only 10-15% of these are functional. The majority present with hypercalcaemia or an incidental neck lump. The key to diagnosis is a markedly raised PTH level in fluid aspirated from the cyst. Only 29% of lesions are positively identified on isotope MIBI scan. Non-functional cysts can be treated through aspiration and ethanol ablation. Functional lesions require excision, indication for which is the same as functional parathyroid adenomas. Malignant transformation is rare.