Fetal adenoma of the thyroid. A common source for false-positive thallium-201/technetium-99m pertechnetate subtraction parathyroid scintigraphy.

The specificity of thallium/technetium imaging for the localization of parathyroid tumors has remained high. False-positive findings usually arise from an incorrectly perceived mismatch. In these case reports, false-positive findings resulted from the presence of intrathyroidal fetal adenomas. Benign thyroid adenomas appear to represent a common source of false-positive finding for parathyroid tumor in thallium/technetium imaging.