A Rare Case of a 30-Gram Giant Parathyroid Adenoma Detected by 99mTc-Sestamibi Scintigraphy and Presenting with Pathological Fracture

Abstract

Background: A giant parathyroid adenoma (GPA) is a very rare, benign (non-cancerous) tumor of the parathyroid gland that is significantly larger than a typical parathyroid adenoma, typically weighing more than 3.5 gram. These primarily present not only hyperparathyroidism but also have severe clinical presentations like high serum calcium, alkaline phosphatase and cause significantly severe osteoporosis. These topographies are totally unlike from malignant parathyroid cancer.

Case Presentation: We present here an interesting case and clinical course of a 55 years female patient with GPA. Patient initially came with pain in left leg along with trouble in walking and was afterward diagnosed to have fracture of neck of left femur and reported with high serum calcium and alkaline phosphatase level. On assessment, the patient was found to have hyper parathyroidism with severe hypercalcemia and osteoporosis. Parathyroid Scintigraphy which procedure includes ^99mTcO₄- Thyroid Scan followed with ^99mTc-sestamibi Parathyroid Scan showed tracer localization to inferior aspect of lower lobe of right thyroid gland suggestive of Parathyroid Adenoma. USG neck revealed large multilobulated hypoechoic mass with retro-tracheal extension displacing trachea anterolaterally and esophagus laterally to left side suggestive as parathyroid adenoma. She underwent right inferior parathyroidectomy and a giant parathyroid adenoma (GPA) weighing 30 gram measuring 6.4x3.8x2.2 cm was excised. Histology confirmed parathyroid adenoma with mostly chief cell type. The tumor excision resulted not only substantial decline in PTH levels but also decrease serum calcium and alkaline phosphatase level. She developed severe hungry bone syndrome (HBS) in post operative period. She was treated aggressively for HBS with intravenous calcium gluconate, oral calcium supplements along with calcitriol.

Conclusion: GPA present as distinct clinical entity with features different from both parathyroid adenoma and parathyroid carcinoma. We strongly recommend the use of ^99mTc-Sestamibi parathyroid scintigraphy as a useful and safe examination technique for the diagnosis of parathyroid adenomas.