Introduction: Giant parathyroid adenomas (GPAs), defined as lesions >3.5 g, are rare. Their size, biochemical severity, and compressive features often mimic carcinoma, creating diagnostic and surgical challenges. Case: A 33-year-old female was incidentally found to have hypercalcemia during evaluation after her newborn developed severe hypocalcemic seizures requiring NICU admission. Maternal calcium was 2.95 mmol/L with hypophosphatemia. Subsequent reviews showed persistent hypercalcemia (3.15–3.3 mmol/L), hypophosphatemia (0.32– 0.51 mmol/L), and markedly elevated intact parathyroid hormone (85–96 pmol/L). She had vitamin D deficiency, very high alkaline phosphatase (1,329 U/L), and progressive bone pain with reduced mobility. Bone mineral density revealed Z scores of −2.9 (hip) and −3.3 (lumbar spine). Multiphase computed tomography demonstrated a multilobulated 6.9 cm mass extending from C5 to T2, compressing the esophagus and raising suspicion for carcinoma. Endoscopic evaluation excluded mucosal invasion. She underwent en bloc left inferior parathyroidectomy with hemithyroidectomy. Intraoperative parathyroid hormone fell from 41.7 to 13.4 pmol/L, confirming complete excision. The gland measured 65 × 20 × 15 mm and weighed 18.4 g. Histopathology revealed a hypercellular parathyroid tumor with endocrine atypia but no invasion, consistent with a giant adenoma. Postoperatively, calcium was initially stable (1.99 mmol/L at discharge) but fell to 1.68–1.82 mmol/L at 2 weeks despite high-dose supplementation. Hypocalcemia persisted for 6 weeks, consistent with delayed hungry bone syndrome, likely precipitated by preoperative vitamin D deficiency, markedly elevated alkaline phosphatase, and low bone mineral density. With intensive supplementation, calcium gradually stabilized, and symptoms improved. Conclusion GPAs can closely mimic carcinoma, with endocrine atypia complicating histopathological interpretation. This case illustrates both diagnostic overlap and the unusual, delayed onset of hungry bone syndrome, emphasizing the need for preoperative risk assessment, correction of metabolic deficiencies, and extended postoperative monitoring. Rare presentations such as delayed hungry bone syndrome refine management strategies and improve outcomes in primary hyperparathyroidism.
Parathyroid Neoplasms