Tc-99m-MIBI-Negative Parathyroid Adenoma in Primary Hyperparathyroidism Detected by C-11-Methionine PET/CT After Previous Thyroid Surgery

A 64-year-old woman with previous thyroid surgery developed symptomatic primary hyperparathyroidism, requiring hydration and furosemide. Cervical ultrasonography and an MRI of the neck were inconclusive. Early Tc-99m-methoxyisobutylisonitrile images 15 minutes post injection demonstrated focal uptake in the left lower thyroid lobe consistent with a small thyroid adenoma. Neither subtraction or late planar nor Tc-99m-methoxyisobutylisonitrile-SPECT images identified a focal area of increased uptake. PET/CT with 460 MBq C-11-methionine demonstrated a focal area of increased uptake in the right thyroid bed. Subsequent surgery confirmed a parathyroid adenoma of 1.4 cm in diameter. Histopathologic analysis showed a parathyroid adenoma of chief-cell type.