SAT-759 Ectopic Mediastinal Intrathymic Parathyroid Adenoma

Abstract Disclosure: B. Cunningham: None. S. Mathew: None. M. Acharya: None. C. Sherpa: None. Primary Hyperparathyroidism (PHPT) is a condition in which excess parathyroid hormone (PTH) is produced. This is most commonly due to parathyroid adenoma and rarely due to parathyroid cancer. While the parathyroid glands are commonly located immediately surrounding the thyroid, the glands can be located ectopically in as many as 6-16% of cases. Here we present a case of a patient with PHPT with a mediastinal intrathymic parathyroid adenoma.A 57-year-old male presented to the emergency room for abdominal pain, nausea, and vomiting. He was found to have hypercalcemia with a corrected calcium of 12.8 mg/dL. Intact PTH was also elevated at 397 pg/mL, and phosphorus level was low at 1.6 mg/dL. 25-OH Vitamin D was normal. He was diagnosed with PHPT and treated with IV calcitonin, pamidronate, and IV fluids for acute management of hypercalcemia. CT chest during admission showed a 3 cm anterior mediastinal mass, suspected to be parathyroid tissue. PTH related peptide was negative. Neck ultrasound showed 2 cm TI-RADS 3 nodule in right and 1.5 cm TI-RADS 2 nodule in left lobe of the thyroid. Technetium-99 m-sestamibi scan showed increased uptake in the right inferior thyroid fossa and central upper mediastinum corresponding to the right thyroid nodule and the mediastinal mass seen in CT chest. Patient was referred to ENT and underwent right thyroid lobectomy and resection of the mediastinal mass. Surgical pathology was consistent with intrathymic parathyroid adenoma. Right lobectomy was consistent with oncocytic noninvasive follicular thyroid neoplasm with papillary like nuclear features (NIFTP).Up to 85% of cases of PHPT are due to overactive, solitary adenomas, making this the most common cause. In fewer cases, there can be multiple adenomas present. There are four parathyroid glands which lie superior and inferior to the thyroid. In development, they arise from the third and fourth branchial pouches. The superior parathyroid glands come from the fourth branchial pouch, which is also responsible for producing the thyroid gland. The inferior parathyroid glands however, arise from the third pouch. This is important in our case particularly, as the third pouch is also responsible for producing the thymus glands, located in the anterior mediastinum. Once diagnosed chemically, combination of CT or MRI with technetium 99m scan provides a complete picture of adenoma location.It is important to be familiar with the anatomy and embryology of the parathyroid glands. Recognizing possible alternative locations of the glands can help in management of PHPT and prevent persistent disease. Hipp I, Khrupovich L, Hrygoriv L, et al. Ectopic parathyroid adenoma in thymus. Int J Radiol Radiat Ther. 2017;3(4):258-259. DOI: 10.15406/ijrrt.2017.03.00069 Presentation: Saturday, July 12, 2025