ODP098 Hyperparathyroidism Caused by Two Large Water Clear Cell Adenomas

BACKGROUND: In ambulatory settings, primary hyperparathyroidism is the most prevalent cause of hypercalcemia. Approximately 85% of primary hyperparathyroidism cases are caused by a solitary parathyroid adenoma; other causes include diffuse parathyroid hyperplasia, multiple parathyroid adenomas, and parathyroid cancer. Chief cell adenomas are the most prevalent; adenomas can also consist of oxyphil cell adenomas, lipoadenomas, or mixed cell adenomas. Water clear cell adenoma (WCCA) is a rare tumor formed of large clear cells with foamy pink cytoplasm. Fewer than 30 cases have been recorded in the literature. CASE: A 52-year-old male with polyuria and polydipsia, diagnosed with hypercalcemia was referred to an endocrinologist. His calcium was 10.9 mg/dl, corresponding parathyroid hormone (PTH) 74 pg/ml, 24-hour urine calcium 818 mg/24hr, vitamin D 25–hydroxy 24.2 ng/ml. He was referred to an endocrine surgeon. A 4-dimensional CT scan revealed soft tissue masses posterior to the thyroid and in the tracheoesophageal groove, consistent with potential parathyroid masses. In the operating room, baseline intraoperative PTH (ioPTH) was 371 pg/ml. A large left superior gland was removed from its normal position, and the ioPTH dropped to 104 pg/ml at 10 minutes post-resection, followed by a rise to 525 pg/ml. A large descended (ectopic) right superior gland was then identified and resected, and the ioPTH decreased to 72, 44, and 57 pg/ml at 10, 15 and 20 minutes post-resection. The remaining parathyroid glands were not identified due to adipose tissue in the neck and likely gland suppression in the setting of high PTH. The pathology report of the two excised glands (left superior 3.2×1.7×0.5cm and 3.703g, right superior 3.4×1.3×0.4cm and 1.86g) demonstrated water clear cell tissue. Post-operatively, patient's polyuria and polydipsia resolved. Labs collected 3 months after surgery demonstrated normalization of the calcium and PTH. The patient was advised to continue follow up every six months. CONCLUSION: Water clear cell parathyroid adenomas are extremely rare. Water clear-cell lesions are considered indolent because excised adenomas are markedly larger than conventional adenomas and grow to a considerable size before becoming biochemically active and diagnosed. Clinical presentation of water clear cell parathyroid lesion is like other causes of primary hyperparathyroidism. The only way to diagnose is via histopathological examination. In rare cases, clear cell renal carcinoma can metastasize to the parathyroid gland causing a similar presentation. Additionally, the rate of hypercalcemia recurrence is higher in WCCA as compared to chief cell adenoma. Therefore, closer follow up of these patients is recommended. Reporting additional cases will aid in our understanding of this uncommon entity, elucidating possible causes/associations, natural history, typical appearances, and post-treatment prognosis. Presentation: No date and time listed