Tc-99m MIBI scintigraphic detection of metastatic insular thyroid carcinoma.

Thallium-201 and, recently, Tc-99m MIBI have been used in conjunction with I-131 scintigraphy for follow-up of patients with well-differentiated thyroid cancer. Insular carcinoma of the thyroid is a fairly aggressive thyroid neoplasm that is believed to arise from follicular cells and usually concentrates I-131. The authors report a patient with recurrent insular thyroid carcinoma in whom bilateral adrenal and lung metastatic lesions developed 3 years after ablative I-131 therapy for cervical lymph node and skeletal metastases. Tc-99m MIBI planar and SPECT images demonstrated these new lesions better than pretherapy I-131 scintigraphy and affords an imaging technique for post-I-131 therapy follow-up that does not require withholding thyroid hormone suppression.