Discordant uptake of Tl-201 and Tc-99m MIBI in a patient with follicular adenoma

Two phase Tl-201 and Tc-99m MIBI thyroid scintigraphies were carried out in a 30-year-old woman who had a solitary cold thyroid nodule seen on a pertechnetate scan. Although an early Tl-201 thyroid image showed intense uptake in the nodule, Tc-99m MIBI demonstrated a hypoactive lesion on the early image. Delayed thyroid scans showed faster washout from the nodule compared to normal thyroid tissue for both Tl-201 and Tc-99m MIBI. Later on, the patient was operated on and the nodule was found to be a follicular adenoma by histopathological diagnosis