Abstract
A 64-year-old male was referred to our hospital with hypercalcemia and elevated serum parathyroid hormone level. Neck USG revealed two hypoechoic solid masses in the right thyroid lobe, but no swollen parathyroid glands in the normal location. 99mTc-sestamibi (MIBI) scintigraphy revealed slight MIBI accumulation in the right thyroid lobe. Based on these findings, a diagnosis of intrathyroidal parathyroid adenoma causing primary hyperparathyroidism was suspected, and right thyroid lobectomy was performed. It was difficult to differentiate intrathyroidal parathyroid adenoma from a thyroid nodule as histopathological examination revealed that the two nodules in the right thyroid lobe showed a follicular architecture. For differential diagnosis between parathyroid adenoma and thyroid nodule, immunohistochemical staining was performed. The upper nodule revealed positive staining for PTH, negative staining for TTF-1 and negative staining for Tg expression, whereas the lower nodule showed negative staining for PTH, positive staining for TTF-1 and positive staining for Tg. Based on the findings, a conclusive diagnosis of intrathyroidal parathyroid adenoma and follicular adenoma of the oncocytic type was made.
