Background and ObjectivesThe American Joint Committee on Cancer (AJCC) staging system 8th Edition has stated that gross extrathyroid extension (ETE) is more important than microscopic ETE, and that it plays an important factor in the classification of T stages. Therefore, the prediction of gross ETE before surgery is important in establishing the clinical stage and determining the surgical extent. However, there are few studies predicting gross ETE using preoperative ultrasonography (US). The purpose of this study is to predict the gross ETE of papillary thyroid carcinoma (PTC) using preoperative US. Subjects and Method The preoperative US findings of 688 patients with PTC were compared with gross ETE confirmed during the surgery. The efficacy of preoperative US was statistically analyzed. Results A total of 70 (10%) patients were confirmed of their gross ETE. Thyroid tumors were classified into three groups (isolation, capsular contact, and capsular protrusion) according to their relationship with capsules, and evaluated using the preoperative US. There was a significant difference in gross ETE between groups (p<0.001). The thyroid tumor that came into contact with the capsule or protruded in the anterior region showed a difference between the capsular contact and capsular protrusion groups (p<0.001), whereas those came into contact with the capsule or protruded in the posterior region showed no significant difference between the two groups (p=0.187). There was no difference in the degree of protrusion (<25%, 25-50%, ≥50%) in the capsular protrusion group (p=0.868), but the difference in tumor size was significant (p<0.001). Conclusion Preoperative US is a useful tool for predicting gross ETE and is more predictable when the thyroid tumor is located anteriorly.
