Diagnostic Accuracy of Ultrasound in Predicting Extrathyroidal Extension and Its Relation to the BMI in North American Population

Abstract

INTRODUCTION: Extrathyroidal extension (ETE) is an important parameter in papillary thyroid carcinoma (PTC) that defines treatment plans. Ultrasound (US) is the current preoperative modality for risk stratification. Previous studies were mostly in Asia, where most of the patients are normal weight. We aimed to examine the effect of body mass index (BMI) on the accuracy of US in North American patients. METHODS: Two authors blinded to the final surgical pathology reviewed the US images of PTC cases. Multiple sonographic features were evaluated including ETE, capsular abutment, bulging of contour, loss of echogenic capsule, and peripheral vascularity. RESULTS: A total of 204 patients with PTC who underwent thyroid surgeries were included. Loss of echogenic capsule rendered the best diagnostic performance (diagnostic odds ratio [ DOR] 4.48, 95% CI 1.86 to 10.78, p = 0.019), with 33% sensitivity and 88% specificity (p < 0.001). Normal weight patients compared with overweight/obese patients had better diagnostic accuracy using the loss of echogenic capsule parameter (DOR 9.67, 95% CI 1.42 to 65.37 vs DOR 3.65, 95% CI 1.29 to 10.29, p = 0.010) with 66.6% vs 30% sensitivity (p = 0.007) and 82.8% vs 89% specificity (p = 0.14). The area under the curve (AUC) for ETE, capsular abutment, bulging of contour, loss of echogenic capsule, and peripheral vascularity represented differential diagnostic accuracy according to the BMI; AUC in normal weight patients was 0.71 ± 0.06, far higher than 0.43 ± 0.05 in obese patients (p < 0.001). CONCLUSION: Use of ultrasonography is associated with low accuracy in predicting ETE in overweight and obese patients. Herein, for the first time, we show the effect of BMI on the accuracy of the US in predicting ETE.