MON-492 Should Isthmic Thyroid Nodule Be Included in ACR TI-RADS Points in Predicting Thyroid Cancer?

Abstract

Background: Thyroid nodules are routinely evaluated with ultrasound. Isthmic nodules carry higher risk of malignancy (in press). Surgical studies suggest higher risk of metastasis from thyroid cancer located in isthmus region. In this study, we evaluate how adding an extra point for isthmic location to current ACR-TIRADS will affect the sensitivity and specificity to predict thyroid cancer.Methods: We performed a subanalysis of isthmic nodules contained in a retrospectively created database of 3313 adult patients from six referral centers with confirmed benign or malignant nodules. Sensitivity and specificity were calculated using the current ACR TI-RADS scoring system and compared to a system that would add an extra point based on nodule location in the isthmus.Results: There were 195 nodules in the isthmus (34 malignant). If a recommendation for FNA was considered a positive test result, the sensitivity and specificity would be 50% (17/34) and 61% (99/161) respectively using current ACR TI-RADS scoring. If an additional point was added the sensitivity and specificity would be 62% (21/34) and 36% (58/161) respectively. Adding the additional point would lead to detection of 4 additional malignant nodules at the cost of biopsying 41 additional benign nodules. If a recommendation for either FNA or follow-up ultrasound for 5 years was considered a positive test result, the sensitivity and specificity would be 82% (28/34) and 35% (56/161) respectively using current ACR TI-RADS scoring. If an additional point was added the sensitivity and specificity would be 94% (32/34) and 15% (24/161) respectively. Adding the additional point would lead to detection of 4 additional malignant nodules at the cost of either biopsying or following 32 additional benign nodules.Conclusions: Isthmic nodules are more likely to be malignant than nodules in other locations. When using the ACR TI-RADS, adding a point for isthmic nodules improves detection of cancer with a moderate increase in the rate of FNA and follow-up of benign nodules. Given the higher risk of extra thyroidal extension and nodal metastases for isthmic cancers, this tradeoff between sensitivity and specificity may be acceptable and should be considered when dealing with nodules in the isthmus.Keywords: thyroid nodule, ACR TI-RADS, location, isthmus, thyroid cancer