IS Case 613: Ectopic intrathymic parathyroid adenoma in the anterior mediastinum
Imaging Sciences URMC 2011
Publication Date: 2011-12-12
The patient is a 44-year-old male presenting with primary hyperparathyroidism (PTH 886.5) and hypercalcemia (Ca 14.9). The patient had been relatively asymptomatic with the only complaint of excessive thirst requiring 1 gallon of water per day. Denied history of renal stones or fractures.
Primary hyperparathyroidism is a disease of excessive PTH secretion resulting in hypercalcemia. Clinical presentations are often asymptomatic and incidentally discovered on routine lab tests, however known complications of hyperparathyroidism are renal stones, polyuria, constipation, fatigue, depression, bone pain and demineralization. Causal breakdown of hyperparathyroidism shows: 80-85% due to a parathyroid adenoma, 12-15% due to hyperplasia, and 1-3% due to parathyroid carcinoma.
“About 80-85% of parathyroid adenomas are found adjacent to the thyroid, but the remainder are ectopically placed and may be within the anterior or posterior superior mediastinum, within or next to the thymus, along the esophagus, along the carotid sheath, or even at the carotid bifurcation. This variation results in 5% of hyperfunctioning parathyroid lesions being missed at the initial surgical procedure.” 
Sestamibi localizes to mitochondria within the parathyroid and thyroid tissue. Thyroid activity rapidly diminishes with time, whereas parathyroid activity remains for longer durations. Early images are acquired at 20 minutes and delayed images acquired at 2-3 hours. Persistent radiotracer activity within the parathyroid glands on delayed images represents hyperfunctioning glands. For evaluation of ectopic parathyroid glands imaging with a larger field of view can be utilized to include the mediastinum.
Preoperative sestamibi-iodine subtraction scanning and neck ultrasonography have been used to locate parathyroid adenomas in an effort to decrease the invasiveness of surgery, locate ectopic glands, and to characterize any lesions in the thyroid gland. CT or MRI can be used to further delineate anatomy prior to operating on an ectopic parathyroid adenoma.
- Mettler FA Jr, Guiberteau MJ. Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, 2005:96.