Evaluation of thyroid nodules with technetium-99m MIBI and technetium-99m pertechnetate

Most thyroid centers use fine-needle aspiration (FNA) and technetium-99m pertechnetate for the preoperative assessment of thyroid nodules. This approach is sufficient in most cases other than follicular neoplasm, and follicular carcinoma is more common than papillary carcinoma in developing countries such as in our center. Technetium 99m-methoxyisobutylisonitrile (MIBI) proposed for myocardial perfusion was also found to be taken up by a variety of tumors including thyroid cancer.

We evaluated MIBI uptake of nodular thyroid disease and compared it with pertechnetate scan, FNA, and histologic findings for the differentiation of malignant thyroid nodules from benign lesions. Seventy-one patients were included in the study. Three-phase pertechnetate scintigraphy was completed after a single injection of 150 MBq. Perfusion/uptake mismatch (uniform perfusion with cold uptake) was regarded as positive for malignancy, whereas perfusion/uptake match (cold perfusion with cold uptake) was regarded as negative. After 1 week, 400 MBq of MIBI was injected, images were obtained at 20 minutes and 2 hours, and evaluated semiquantitatively by use of a 4-point (0-3) scoring system. MIBI scans were considered positive if there was uptake superior to normal thyroid tissue on early and delayed images (score = 3). In the following days and weeks, all patients underwent FNA followed by surgery.

Histopathologic diagnosis revealed a total of 23 thyroid carcinomas, 21 (91%) and 19 (83%) were positive on MIBI and pertechnetate, respectively. Of the 48 patients with benign nodules, 11 (23%) and 29 (60%) were positive on MIBI and pertechnetate, respectively. The specificity of MIBI, pertechnetate, and FNA is 77%, 40%, and 90%, respectively.

In combination with FNA and three-phase pertechnetate scan, MIBI could be helpful in preoperative assessment of thyroid nodules. Intense MIBI activity increases the probability of thyroid cancer, whereas reduced activity drastically decreases the probability of malignancy.