Differentiation of parathyroid and thyroid nodule is often difficult even with aids of ultrasonography and computed tomography. Tc-9m sestamibi (MIBI) scintigraphy is useful in the detection of hyperfuntioning parathyroid nodules. However, its role in the differentiation between parathyroid and thyroid nodules including malignancies is not well studied. Therefore, the purpose of this study is to evlauate the role of Tc-99m MIBI imaing in the differentiation of parathyroid adenoma from thyroid malignancy.

Six patients (4 women, 2 men, mean age 43 years) with parathyroid adenoma and 4 patients (2 women, 2 men, mean age 56 years) with thyroid papillary cancer were enrolled. Ten and 180 minutes after injection of 740 MBq Tc-99m MIBI, pinhole image of the anterior neck was obtained. Nodule-to-thyroid ratio (N:T) was measured from same sized region of interests over nodule and normal thyroid bed. Retention Index (RI) was calculated as N:T 10 minus N:T 180 divided by N:T 10.

as those with thyroid cancer (1.09 ± 0.35, 1.24 ± 0.36, respectively, P>0.05 ). However, RI of parathyroid patients was higher than thyroid cancer patients (0.64 ± 0.29, -0.12 ± 0.20, respectively, P<0.05).

Parathyroid adenoma showed higher retention rate of Tc-99m MIBI than thyroid cancer. Therefore, differntiation of parathyroid and thyroid nodule could be possible using Tc-99m MIBI scintigraphy.