Background: Ultrasonography (US) changes have been noted in patients with autoimmune thyroiditis (AT). Here, we report that some patients with late stage AT have a distinctive, previously unreported finding on US that we call the "hypoechoic triangle sign" (HET). Methods: On US, the HET sign was characterized as a well-defined area of low echogenicity, about 10 mm in diameter, between the lateral margin of one or both thyroid lobes, the medial wall of the carotid artery, and, posteriorly, the prevertebral muscles. Twenty-six patients with AT who had the HET sign (Group 1) were compared with 71 patients with AT who had normal serum thyrotropin (TSH) and free thyroid hormones levels (Group 2) and with 154 normal controls (Group 3). TSH was tested at least twice, first as part of their regular clinical care and then in follow-up. The groups were similar in terms of age, sex, and body mass index. Thyroid volume by US, TSH, free triiodothyronine, free thyroxine, antithyroid antibodies, and l-thyroxine treatment were evaluated. Sonographic gray-scale analysis and three-dimensional reconstruction of HET region were performed in five of the Group 1 patients. Results: Thyroid volume was significantly smaller (p <0.01) in Group 1 than in Groups 2 and 3 (6.9 ± 2.18 vs. 10.4 ± 2.1 and 9.8 ± 2.5 mL, respectively). In Group 1, 61.5% of subjects were taking l-thyroxine for hypothyroidism; none of the Group 2 or 3 patients was taking thyroid hormone. Serum TSH was significantly higher (p <0.01) in Group 1 versus Groups 2 and 3 (3.6 ± 1.3 vs. 2.18 ± 1.4 and 1.9 ± 1.1 mIU/L, respectively). None of the Group 2 or 3 patients had the HET sign. Gray-scale US demonstrated an overlap between HET zone and the surrounding muscle tissue. Conclusions: The HET sign seems to be specific for overt thyroid failure in patients with AT as it was not noted in patients with AT not having overt thyroid failure. The incidental finding of the HET sign during cervical US examination should prompt obtaining thyroid function tests to rule out hypothyroidism. Our study provides data regarding specificity but not sensitivity of the HET sign for AT and thyroid failure because a consecutive group of AT patients with thyroid failure was not studied. In addition, the specificity of the HET sign for AT needs to be evaluated further by studying a diverse group of thyroid diseases.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism