Reconfirmation of the accuracy of the taller-than-wide sign in multicenter collaborative research in Japan.

The taller-than-wide sign indicates that the anteroposterior dimension-to-transverse dimension ratio (AP/T ratio) is higher than 1. The aim of the present study was to reconfirm the accuracy of the taller-than-wide sign for diagnosing malignant thyroid nodules by ultrasonography in multicenter collaborative research, and investigate differences according to tumor sizes, histological types, and the influence of the tilt and orientation of the probe. At 6 registered institutes, 2,032 thyroid nodules were successively operated on and diagnosed pathologically. The accuracy of the taller-than-wide sign for diagnosing malignant tumors by ultrasonography was retrospectively analyzed across all nodules as well as in analyses separately stratified by tumor size and histology. The influence of the tilt and orientation of the probe was also assessed. The taller-than-wide sign showed high specificity for diagnosing malignancy in all nodules tested. It also showed high specificity regardless of the tumor size. When tumors were analyzed by histological types, the AP/T ratio of papillary carcinoma was significantly higher than that of benign nodules, whereas no significant difference was observed between follicular carcinoma and benign nodules. The specificity of longitudinal sections was significantly higher, while the AUC of longitudinal sections was significantly larger than those of transverse sections. The AP/T ratio obtained when the probe was tilted was not significantly different from that when it was straight. The present results support the usefulness of the taller-than-wide sign for diagnosing malignant tumors regardless of size, but not follicular carcinoma. The influence of the tilt and orientation of the probe was negligible.