Ultrasound risk evaluation of thyroid nodules that are "unspecified" in the 2015 American Thyroid Association management guidelines A retrospective study

This study sought to assess the malignant risks of "unspecified" thyroid nodules; that is, nodules that were not of a type described in the 2015 American Thyroid Association (ATA) guidelines. We retrospectively reviewed medical records and ultrasound (US) data for 1808 consecutive patients with 2614 thyroid nodules who underwent thyroidectomy between January 2015 and December 2015. Nodules with US features that did not satisfy the criteria for any risk category in the 2015 ATA guidelines were defined as "unspecified" nodules. These thyroid nodules were retrospectively assessed using the Thyroid Imaging, Reporting and Data System proposed by Kwak (Kwak-TIRADS) and the American College of Radiology Thyroid Imaging, Reporting and Data System (ACR-TIRADS). There were 70 "unspecified" nodules (2.7%, 70/2614), and 18.6% (13/70) of these nodules were malignant. The percentages of nodules with Kwak-TIRADS grades 4a, 4b and 4c were 53.3%, 40.0%, and 6.7%, respectively. The percentages of nodules with ACR-TIRADS grades TR2, TR3, TR4, and TR5 were 5.7%, 2.9%, 70.0%, and 21.4%, respectively. Among the "unspecified" nodules, there were significantly more nodules in Kwak-TIRADS categories 4b and 4c in the malignant pathology group than in the benign pathology group (P<.01). Our results imply that "unspecified" thyroid nodules based on the ATA guidelines could partly be evaluated using the Kwak-TIRADS and that the ATA guidelines could incorporate more accurate malignant risk stratification.