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2 Responses to “Trapping-only-nodules”

  1. Werner Says:

    Thyroid: 2006 Aug;16(8):757-62.

    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.

  2. Werner Says:

    On the other hand, most benign and malignant nodules have less uptake than the surrounding thyroid tissue (“cold” nodules). Three to eight per cent of thyroid nodules absorb 99Tc, but not 123I. They may appear hot or warm on 99Tc SC and cold on late (24 hours) 123I or 131I SC.99,100,108,109 This is known as the “trapping-only phenomenon”. Although such nodules carry a risk of malignancy, they are usually benign.108-114 Therefore, it is recommended by some authors that patients with hot or warm nodules on 99Tc SC undergo 123I SC,110,115 especially if serum TSH is not suppressed.109

    SC has several limitations. Firstly, it has limited value in selecting patients for surgery because of its low specificity. In a study, only one-half of excised thyroid malignancies appeared cold on SC.103 Secondly, due to the fact that it is a two-dimensional technique, there is superimposition of abnormal nodular tissue and normal thyroid tissue.9 On account of such superimposition, small non-functioning nodules may appear warm rather than cold.103 Finally, if the production of thyroid hormone by a functioning nodule is insufficient to suppress TSH secretion, the functioning nodule may appear warm rather than hot.100,101

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