Limitations of parathyroid imaging with Tc-99m/Tl-201 subtraction and early/delayed Tc-99m MIBI imaging

An 87-year-old women with recurrent gastric ulcers was admitted with isolated hypercalcemia and thyroid enlargement. Serum PTH was 88.8 pg/mL (normal, 3-40 pg/mL) and ionized calcium 12.2 mg/dl (normal, 8.9-10.5 mg/dl). The patient was euthyroid. Ultrasonography showed a hyporeflective node in the thyroid bed, and CT showed a retrosternal goiter with trachea deviation. Dual-isotope scintigraphy and early/delayed Tc-99m MIBI imaging suggested a neoplasm. At surgery, a 1 cm left upper parathyroid adenoma and a benign microfollicular thyroid adenoma were found. Both examinations failed to detect the parathyroid adenoma, and incorrectly identified the right lobe mass as malignant.