TC-99M MIBI ACCUMULATION IN REMNANT THYMUS - A CAUSE OF FALSE-POSITIVE INTERPRETATION IN PARATHYROID IMAGING

A 17-year-old boy, who was suspected of having hyperparathyroidism, was admitted for parathyroid imaging. Tc-99m pertechnetate Tc-99m MIBI subtraction scintigraphy was performed. A focal increased activity accumulation was observed visually after Tc-99m MIBI injection in the lower left lobe of the thyroid extending inferiorly, which was interpreted as parathyroid adenoma. At surgery, a left thyroidectomy was performed and no parathyroid abnormality was observed, but a 3 x 2 x 3 cm mass, which was thought to be a thymic remnant, was removed. Histopathologic examination of this specimen revealed an involuted thymic tissue. Three months after surgery, Tc-99m MIBI imaging was repeated and no activity accumulation was seen in the neck.