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

Background. Most thyroid centers use fine-needle aspiration (FNA) and techn etium-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 develop ing countries such as in our center. Technetium 99m-methoxyisobutylisonitri le (MIBI) proposed for myocardial perfusion was also found to be taken up b y a variety of tumors including thyroid cancer. Methods. We evaluated MIBI uptake of nodular thyroid disease and compared i t with pertechnetate scan, FNA, and histologic findings for the differentia tion of malignant thyroid nodules from benign lesions. Seventy-one patients were included in the study. Three-phase pertechnetate scintigraphy was com pleted after a single injection of 150 MBq. Perfusion/uptake mismatch (unif orm perfusion with cold uptake) was regarded as positive for malignancy, wh ereas perfusion/uptake match (cold perfusion with cold uptake) was regarded as negative. After 1 week, 400 MBq of MIBI was injected, images were obtai ned 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 fol lowed by surgery. Results. Histopathologic diagnosis revealed a total of 23 thyroid carcinoma s, 21 (91%) and 19 (83%) were positive on MIBI and pertechnetate, respectiv ely. Of the 48 patients with benign nodules, 11 (23%) and 29 (60%) were pos itive on MIBI and pertechnetate, respectively. The specificity of MIBI, per technetate, and FNA is 77%, 40%, and 90%, respectively. Conclusions. in combination with FNA and three-phase pertechnetate scan, MI BI 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. (C) 2001 John Wiley & Sons, inc.