Ectopic parathyroid adenoma in the posterior triangle of the neck

Ectopic parathyroid adenomas are a major cause of persistent hyperparathyroidism. They can be located anywhere from the base of the tongue to the mediastinum. We describe a patient with hyperparathyroidism from an adenoma in a supernumerary gland located in the left posterior triangle of the neck, outside of the carotid sheath.