Hyperfunctioning intrathyroid parathyroid gland: a potential cause of failure in parathyroid surgery.

Four patients with hyperfunctioning intrathyroid parathyroid are reported. In each case the intrathyroid parathyroid was embedded within the thyroid parenchyma and appeared as a solitary 'cold' thyroid nodule by radioactive iodine scanning. It is believed that the intrathyroid parathyroid evolves as the lateral lobe of the thyroid fuses with the isthmus in the early development of the thyroid. Embryologically, and intrathyroid parathyroid is thus likely to be the superior gland. When the superior parathyroid gland is missing at the time of exploration, a nodule within the ipsilateral lobe of the thyroid may well be an intrathyroid parathyroid. Under these conditions, lobectomy for the exclusion of such a gland is mandatory.