A 65 year old woman with history of chronic renal failure and tertiary hyperparathyroidism has undergone a four-gland parathyroidectomy several months ago. She presents with persistently elevated serum calcium and PTH.
She is referred for a Tc99m sestamibi parathyroid scan.
This is a patient with an ectopic mediastinal parathryoid adenoma.
The patient also had an arterial phase chest CT.
The CT demonstrates an avidly enhancing soft tissue nodule in the anterior mediastinum adjacent to the aorta and left innominate vein.
The SPECT data can also be combined with the contrast CT using a software fusion:
A fifth supernumerary parathyroid gland occurs in 3-10% of individuals. The suPerior parathyroid glands (normally posterior to the upper/mid thyroid) arise embryologically from the fourth branchial pouch, and descend inferiorly and Posteriorly. The inferior parathyroid glands (normally adjacent or just inferior to the lower thyroid poles) arise from the third branchial pouch, and descend inferiorly and anteriorly. Therefore this adenoma in the anterior mediastinum likely represents an ectopic inferior gland.
The surgical implication is that superior glands are usually posterior to the recurrent laryngeal nerve (and thus may have greater risk of nerve injury during resection).
Ziessman HA, O’Malley JP, Thrall JH, eds. Nuclear Medicine, the Requisites, 4th ed. Philadelphia: Elsevier, 2014.
