Thyroid Hemiagenesis by I-123 Thyroid Scan with High-Resolution Real-Time Ultrasound Confirmation

I-123 thyroid scans were performed on two female patients who both presented with the history of an enlarged right thyroid lobe on routine physical examination. Both studies showed unilateral uptake of I-123 on the right with no uptake on the left. The differential diagnosis of unilateral uptake includes postsurgical, hyperfunctioning autonomous adenoma, thyroiditis, hemiagenesis, abscess, postirradiation, colloid cyst, or some type of benign or malignant tumor (1). Results of thyroid function tests and iodine 4-hour and 24-hour uptakes were normal. Neither patient had prior thyroid surgery. The ultrasound examinations demonstrated an absent left lobe and a normal right lobe in both cases, therefore making the diagnosis one of hemiagenesis. Various other techniques have been recommended in the past to evaluate unilateral thyroid uptake of radiopharmaceu-tical, including the thyrotropin stimulation test, Tc-99m pertechnetate thyroid angiography, TI-201 scintigraphy, and, more recently, Tc-99m methoxyoisobutyl isonitrile (MIBI) (2,3). Current state-of-art, high-resolution, realtime ultrasound, now widely available, is much less operator dependent than in the past, requiring only minimal expertise to evaluate for the presence of thyroid tissue. Ultrasound, rapid and radiation-free, should be the preferred modality to confirm the diagnosis of the uncommon entity, thyroid hemiagenesis (4).