Retropharyngeal Ectopic Parathyroid Adenoma: A Case Resolved with 18F-Fluorocholine Positron Emission Tomography (PET)

Primary hyperparathyroidism is caused by either adenoma or hyperplasia involving the chief cells of parathyroid glands. Primary hyperparathyroidism is third most common endocrine disease affecting women 2-3 times more often than men. The incidence of Primary Hyperparathyroidism (PHPT) is increasing with rate of 42:100,000 per year. Both parathyroid adenoma or hyperplasia is surgically curable, but the real twist lies in pre-operative localization. The usual pre-operative localization of PHPT is done by two modalities namely cervical ultrasound and SestaMIBI scan. Cervical ultrasound is cheap and easily available and can simultaneously detect any thyroid pathology if present. The radionuclide imaging is particularly useful in identification of ectopic glands as well as easier recognition of posteriorly located upper glands. When both modalities are used together it increases the sensitivity of pre-operative localization of the glands. Primary hyperparathyroidism due to ectopic parathyroid adenoma is seen in 16-23% of cases. We report a case of a 55-year-old female who presented with elevated calcium levels on routine investigations. She had bilateral renal calculi with a serum calcium level of 11.8 mg/dL and an iPTH level of 98.1 pg/mL. Ultrasound of the neck revealed a hyperechoic nodule in the inferior pole of the left lobe of the thyroid, suspicious for a parathyroid adenoma and sestamibi confirmed the lesion on right side. She underwent a right inferior parathyroidectomy, but her iPTH levels were persistently elevated postoperatively. She was further evaluated for hyperparathyroidism with an 18-F fluorocholine Positron Emission Tomography (PET) scan, which revealed a right retropharyngeal parathyroid adenoma. She underwent re-exploration of the neck and removal of the parathyroid adenoma. Intra-op iPTH dropped to normal levels. The histopathological findings were consistent with parathyroid adenoma. Patient is in follow-up with normal calcium and iPTH levels.