Endocrine Abstracts

JOINT2591

Introduction: Trapping-only nodules, or “discordant” nodules, are thyroid nodules that exhibit increased uptake of radioiodine and decreased uptake of technetium-99m on thyroid scans. Unlike regular “hot” nodules, which actively synthesize and secrete thyroid hormones, trapping-only nodules simply trap the iodine but there is no organification or increased hormone synthesis, and consequently there is no hyperfunction. It has previously been proposed that this trapping-only phenomenon might be associated with higher risk of malignancy, and thus, these nodules often require careful evaluation.

Aim: Evaluate the risk of malignancy of trapping-only nodules.

Methods: All thyroid scans performed in our center from January 2020 to June 2024 reporting trapping-only nodules were reviewed (n = 133). Subsquently, pathology results from all the nodules that underwent fine-needle aspiration cytology and/or surgery were examined (n = 41). Characteristics of the nodules on ultrasound were also collected.

Results: Thirty-nine patients with 41 trapping-only nodules were included, 66.7% were female and the mean age was 59.0±12.9 year. Thirty-one (75.6%) had subclinical thyrotoxicosis, and TSH nadir was 0.17±0.13 mU/l. Twenty-five (64.1%) had uni- or multinodular toxic goiter and 8 (20.5%) had Graves’ disease. Regarding ultrasound characteristics, the mean size of the nodules was 21.2±9. 9 mm, and most were classified as EU-TIRADS 3 (56.1%) and EU-TIRADS 4 (36.6%). Of the 33 nodules that underwent fine-needle aspiration cytology, 26 (78.8%) were benign, 5 (15.2%) were nondiagnostic, and 2 (6.0%) were suspicious for malignancy, according to the Bethesda system. Of the 14 patients that underwent surgery, 6 (75.0%) had pathology findings consistent with thyroid follicular nodular disease, 1 (12.5%) had a single adenomatous nodule, and 1 (12.5%) had a hyalinizing trabecular tumor, which is a low-risk follicular cell-derived neoplasia. Six nodules had both results from aspiration cytology and surgical histology. Of note, of the two patients with nodules suspicious for malignancy, one had follicular nodular disease and the second had the hyalinizing trabecular tumor.

Conclusion: Trapping-only nodules do not appear to carry an increased risk of malignancy, and their evaluation should be similar to “cold” nonfunctioning nodules. Larger studies are needed to assess the true prevalence of thyroid malignancy among trapping-only nodules.