The glandular structures of the neck are derived from the lining of the gut tube, the thyroid from the base (foramen cecum) of the tongue, and the parathyroids and thymus from the branchial pouches of the embryonic neck. Inferior parathyroid and thymus arise from pouch III, while the superior glands come from IV. The parathyroids are most often (80%) near the posterior capsule of the thyroid gland.
The superior gland commonly lies near the cricothyroid junction. It is sometimes difficult to tell a normal, small parathyroid gland from a thyroid nodule or a lymph node. The healthy gland is tan to brown and turns black when its delicate blood supply is compromised. This is not a recommended way to identify it. Meticulous dissection is necessary.
The inferior parathyroids are most often below the inferior thyroid artery and anterior to the recurrent nerve. They are more variable in their location than the superior glands, and may be found in the thyro-thymic ligament or in the thymus substance because of their common origins. Parathyroids are occasionally located within the substance of a thyroid lobe. Radionuclide tracer localization of parathyroid tissue has taken some of the guesswork out of parathyroid exploration and also allowed minimally invasive parathyroidectomy when a single adenoma is suspected.