Serendipitous diagnosis of hyperthyroidism on pulmonary perfusion scintigraphy

Pulmonary perfusion scintigraphy in a 28-year-old woman being evaluated for suspected pulmonary embolism showed no pulmonary abnormalities, but demonstrated diffusely increased activity in an enlarged thyroid gland on the Tc-99m macroaggregated albumin images. There was no history of prior radiopharmaceutical administration. Absent activity in the brain excluded a right-to-left shunt. Thus, the thyroidal uptake procedure likely indicated uptake of free Tc-99m pertechnetate in the 2-hour-old radiopharmaceutical preparation. The considerably higher thyroid uptake relative to gastric, renal, and salivary gland uptake suggested a hyperfunctioning thyroid, with increased trapping of Tc-99m pertechnetate. A diagnosis of hyperthyroidism was confirmed by thyroid function testing.