Thallium-pertechnetate subtraction scintigraphy: a quantitative comparison between adenomatous and hyperplastic parathyroid glands.

In a prospective study of 201Tl-99mTc subtraction scintigraphy, 61 hyperparathyroid patients were investigated prior to neck exploration. At surgery, 46 adenomatous and 28 hyperplastic parathyroid glands were excised. We examined the relationship between the pathological category of these glands, their mass, uptake of 201Tl thallous chloride, and the frequency of true-positive and false-negative scintigraphic findings. The variation of sensitivity with parathyroid mass was found to be similar for both adenomatous and hyperplastic glands, with a detection threshold that lay in the range 0.3-0.8 g. The higher overall sensitivity for the detection of adenomas (85%) compared with hyperplasias (44%) was due to the smaller mean weight of the latter. When the parathyroid uptake of thallium was quantified scintigraphically, the practical detection limit of subtraction scanning was found to be an uptake of 0.015%. For glands greater than 1.5 g in weight, uptake increased linearly with mass, and specific uptakes were within the range 0.01-0.04%/g. Below lg, certain small glands had much higher specific uptakes, up to 0.2%/g. The range of specific uptakes found was similar for both adenomatous and hyperplastic categories. Multinodular or diffuse goitre was a cause of failure in 10% of investigations. In a further 5%, a solitary thyroid nodule gave rise to a false-positive result.