A Case Report of an Ectopic Mediastinal Parathyroid Adenoma that was Challenging to Locate

Introduction:
Primary hyperparathyroidism from an ectopic parathyroid adenoma can pose diagnostic and management challenges when several different imaging modalities do not localize the adenoma and when it is not found on surgical exploration.

Case Description:
We report a case of a 69 years old Caucasian female with history of primary hyperparathyroidism complicated by the inability to localize the adenoma despite several imaging modalities. She underwent neck exploration twice by two different surgeons who were unable to locate a parathyroid adenoma.

She underwent 2 separate parathyroid nuclear medicine scan with single photon-emission computed tomographic (SPECT) of the neck and chest done several years apart. The initial SPECT did not demonstrate a parathyroid adenoma in the neck or ectopically nor did several nuclear medicine scans of the neck.

Ultimately, the 2^nd SPECT of the neck and chest was able to detect a contrast-enhanced mass in the mediastinum. She was referred to a thoracic surgeon who was able to remove the ectopic parathyroid adenoma robotically. The histopathology of the mediastinal mass was consistent with a parathyroid adenoma. She was discharged home from the hospital on calcium and calcitriol supplementation. Her calcium normalized and she ultimately was able to come off calcium and calcitriol supplementation. Calcium and PTH have remained normal several months after surgery.

Discussion:
The incidence of ectopic parathyroid glands is approximately 25%. In primary hyperparathyroidism approximately 6-16% of adenomas are located ectopically. Surgical intervention is the mainstay of therapy with preoperative imaging for localization of the adenoma being the standard of care. 4D CT has approximately 85% sensitivity and Sestamibi/SPECT CT has 65% sensitivity for location of a single adenoma with specificity of 92% and 98% respectively. Despite this, in our case the localization of parathyroid adenoma took 7 years, 4 different scans and 3 surgeries in order to successively localize and resect the ectopic parathyroid adenoma.