The aim of this study was to determine the prevalence of trapping-only nodules of the thyroid gland. The study was prospectively performed in patients bearing hot or warm thyroid nodules at pertechnetate scan in the presence of circulating thyrotropin (TSH) within the normal range. The study was restricted to these patients because nodules that suppress TSH are certainly autonomous. In 140 patients showing hot or warm nodules at 30-minute pertechnetate scintigraphy, and normal TSH levels, radioiodine scintigraphy was performed at 24 hours. The trapping-only pattern, i.e., the presence of a cold nodule in late radioiodine scintigraphy was observed in seven patients (5%). Five had benign thyroid nodules, one follicular carcinoma, and one extrathyroid metastases of papillary-follicular carcinoma. Despite controversy on this issue, trapping-only nodules of thyroid should be searched because they have risk of malignancy and must be differentiated from autonomous adenomas at the compensated stage. The search may be limited to patients with normal serum TSH.
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