[Usefulness of 99mTc-MIBI SPECT in the metastatic lesions of thyroid cancer]

99mTc-MIBI is widely used as a tumor-seeking agent for parathyroid tumor, lung cancer, etc. We tried to detect the metastatic lesions of thyroid cancer by 99mTc-MIBI SPECT and evaluated 131I-uptake in the region of 99mTc-MIBI accumulation. Twenty-seven cases of thyroid cancer (23 papillary adenocarcinoma, 3 follicular adenocarcinoma, 1 unknown) were examined by 99mTc-MIBI. All cases were confirmed by surgery. Thyroglobulin was measured in all cases before 99mTc-MIBI SPECT. 131I-therapy (4.5-5.5 GBq) was performed on 24 patients and whole body scintigram was taken 7-10 days after. Thirty minutes after an injection of 99mTc-MIBI (740 MBq), SPECT with a three-head gamma camera was performed. Abnormal accumulation of 99mTc-MIBI was noted in 14 patients, all cases detected on CT or MRI. In 11 of the 13 cases in which accumulation was not visualized, no metastasis was detected. Most cases of abnormal accumulation on 99mTc-MIBI showed a high level of thyroglobulin. Metastatic lesions of follicular adenocarcinoma in three patients (right humerus, axillary region and sternum) showed strong accumulation of 99mTc-MIBI, and 131I was strongly taken up in these lesions. 131I was also taken up in the metastatic lesions of papillary adenocarcinoma with marked accumulation of 99mTc-MIBI. 99mTc-MIBI did not accumulate in a case with diffuse pulmonary uptake of 131I. 99mTc-MIBI SPECT could detect occult metastatic lesions in the soft tissue more clearly than CT or MRI. In conclusion, 99mTc-MIBI study might be useful as a follow-up study of patients after surgery for thyroid cancer.