Ectopic Retropharyngeal Parathyroid Adenoma Causing Primary Hyperparathyroidism

Introduction : Primary hyperparathyroidism (PHPT) is a common endocrine disorder that affects approximately 1-7 cases in every 1000 adults. PHPT mostly presents as a sporadic disease (90%) but may be part of hereditary syndromes. A solitary adenoma is found in > 80% of cases while hyperplasia of all four glands is rare ( < 15%).

Ectopic parathyroid glands usually lie along their embryological path of descent, commonly in thyroid gland or mediastinum, rarely occurring in the pharyngeal region.

We describe a rare case of retropharyngeal parathyroid adenoma in a patient with biochemically confirmed primary hyperparathyroidism.

Case Description : 44-year-old female with history of hypertension, recently diagnosed with primary hyperparathyroidism. She was incidentally found to have hypercalcemia (calcium level 10.1) one year prior, during preoperative bloodwork done for plastic surgery. At that time, she was taking hydrochlorothiazide.  She was advised to discontinue hydrochlorothiazide, however, hypercalcemia increased to 11.8. Detailed lab work revealed elevated intact PTH (97 pg/mL), normal renal function, albumin, phosphorus, and 25 OH -Vitamin D levels.

She had a prior history of renal stones (one episode, around age 20), but no pancreatitis or ulcers.  Her energy level was normal but reported mild decline in memory and concentration. She reported occasional leg, hand, and neck bone pain with no fractures. She denied complaints of hoarseness, dysphagia, or dyspnea, with no history of either radiation exposure or neck surgeries.

Neck ultrasound revealed a retropharyngeal hypoechoic structure measuring 3x3x4 mm suggestive of an enlarged right inferior parathyroid gland. Four-dimension computed tomography (4D-CT), revealed an arterially enhancing circumscribed structure with rapid washout in the right retropharyngeal space, cranial to and adjacent to the posteromedial aspect of the upper pole of the right thyroid lobe measuring 0.7 x 1.8 x 2.7 cm consistent with enlarged parathyroid gland. The patient underwent parathyroidectomy with intraoperative PTH measurements. Baseline PTH was 126 pg/mL prior to surgical manipulation and 30 pg/mL 20 minutes following resection.

Discussion :

Ectopic retropharyngeal parathyroid adenomas are rare and usually associated with severe clinical manifestations. Lack of successful identification may delay the diagnosis and lead to failure in surgical resection.
High-quality localization techniques such as 4D-CT, and magnetic resonance imaging are found to be superior to traditional techniques for localization of affected gland(s) perioperatively. Choice of imaging modality should be individualized with respect to efficacy, cost, and availability in clinical practice.