Significance of extrathyroidal uptake of Tc-99m and I-123 in the thyroid scan: concise communication.

Areas of extrathyroidal uptake were noted on thyroid scans obtained with Tc-99m and I-123 in five subjects. Four of them had palpable lymph nodes corresponding to the extrathyroidal uptake. All the palpable nodes that showed radionuclide uptake contained metastatic thyroid carcinoma, with predominantly well-differentiated follicular cells. Extrathyroidal areas of uptake on a routine thyroid scan with pertechnetate and/or radioiodine most probably indicate thyroid carcinoma with regional metastases.