Giant Functional Parathyroid Cyst With “Snowstorm” Phenomenon: A Rare Clinical and Imaging Presentation

Giant functional parathyroid cysts (PCs) are extremely rare and can present significant diagnostic challenges. We report a case of a 31-year-old woman with primary hyperparathyroidism (PHPT) due to a giant PC, which presented with biochemical features of hyperparathyroidism, compressive symptoms in the neck structures, and a unique ultrasonographic “snowstorm” pattern, mimicking thyroid pathology. Diagnosis was confirmed postoperatively by histopathology. This case highlights the importance of including PCs in the differential diagnosis of cystic neck masses, particularly when biochemical and imaging findings are discordant.