Ultrasound findings of papillary thyroid carcinoma originating in the isthmus: comparison with lobe-originating papillary thyroid carcinoma.

Abstract

The goal of this study was to analyze the differences in ultrasound characteristics of papillary thyroid carcinoma (PTC) originating in the thyroid isthmus versus that originating from the lobes. From a retrospective review of our institution's database of records dated between January 2007 and December 2008, we identified 48 patients with classic PTCs located in the isthmus. All the patients had undergone preoperative ultrasound imaging, total thyroidectomy with bilateral central lymph node dissection, and postoperative follow-up for at least 2 years. As a control group, 96 patients with classic PTCs located in the lobe who had undergone total thyroidectomy with bilateral central lymph node dissection during the same period were randomly matched to the study patients for age, sex, and tumor size. According to the clinicopathologic analyses, the incidence of extrathyroidal extension was higher in the patients with a tumor originating in the isthmus than in the control group (p = 0.026). According to the imaging analyses, the tumors originating in the isthmus more frequently had a circumscribed margin (p = 0.030), a wider-than-tall shape (p < 0.001), and the suspicion of extrathyroidal extension (p < 0.001) than those originating from the lobes. The results of this study showed that PTCs originating in the isthmus were more likely to have extrathyroidal extension than those originating from the lobes. Therefore, careful ultrasound evaluation should be performed on masses in the thyroid isthmus even if ultrasound shows a circumscribed mass with a wider-than-tall shape.