Extrathyroidal extension (ETE) is one of the risk factors to be considered when deciding on operation extent and radioiodine ablation in differentiated thyroid carcinoma. Ultrasonography (USG) is the most widely used imaging modality in preoperative evaluation of thyroid carcinoma; however, few studies regarding accuracy of USG in preoperative evaluation of ETE have been reported. In this study, we investigated the accuracy of preoperative USG in detection of ETE and evaluated other risk factors associated with permanent ETE.

We reviewed the medical records of 349 consecutive patients who underwent curative thyroidectomy for differentiated thyroid carcinoma. Preoperative USG findings according to percent of contact and disruption of thyroid capsule were evaluated and compared with the permanent pathology. Clinicopathologic characteristics were investigated for assessment of the risk factors associated with ETE.

ETE was identified in permanent pathology of 68 (19.5%) patients. When we defined the ETE on preoperative USG as more than 25% contact with the adjacent capsule, the positive predictive value (PPV) and negative predictive value (NPV) were 43.03% and 90.73%, respectively. Size of the nodule and preoperative USG findings with the percent of contact with adjacent capsule and capsule disruption showed an association with ETE on permanent pathology. However, in multivariate analysis, only size of the nodule and capsule disruption on USG were identified as risk factors for prediction of ETE on permanent pathology.

Capsule disruption on preoperative USG can provide useful predictive information about permanent ETE. Another risk factor associated with ETE was size of nodule in differentiated thyroid carcinoma.