Demonstrable photopenic lesion in Tc-99m pertechnetate thyroid imaging after recent contrast radiographic procedure.

Iodine-contained contrast media of a recent arteriogram can block normal thyroid uptake of Tc-99m pertechnetate or radioiodine, resulting in virtual nonvisualization of the thyroid gland and showing a prominent salivary activity. In Tc-99m pertechnetate thyroid imaging, however, diffuse soft-tissue uptake in the anterior neck surrounding a fluid containing (cystic) lesion may standout as photopenia. The authors present two patients with recent contrast radiographic procedures who underwent Tc-99m pertechnetate imagings that demonstrated photopenic lesions: one was a thyroid cyst and the other confirmed an abscess.