Thyroid sonography/ultrasound
Thyroid Ultrasound (US) is a noninvasive imaging technique that should be performed on all patients with nodules suspected clinically or incidentally noted on other imaging studies such as carotid ultrasound, CT, MRI, or 18-FDG-PET scan.
Ultrasound will help confirm the thyroid nodule/s, assess the size, location and evaluate the composition, echogenicity, margins, presence of calcification, shape and vascularity of the nodules and the adjacent structures in the neck including the lymph nodes. If there are multiple nodules, all the nodules should be assessed for suspicious US characteristics.
FNA decision making is guided by both nodule size and ultrasound characteristics, the latter being more predictive of malignancy than size [35, 36]. The nodular characteristics that are associated with a higher likelihood of malignancy include a shape that is taller than wide measured in the transverse dimension, hypoechogenicity, irregular margins, microcalcifications, and absent halo [35–41]. The feature with the highest diagnostic odds ratio for malignancy was suggested to be the nodule being taller than wider [42]. The more suspicious characteristics that the nodule has, it increases the likelihood of malignancy. In contrast, benign nodule predicting US characteristics include purely cystic nodule (?2 % risk of malignancy) [39], spongiform appearance (99.7 % specific for benign thyroid nodule) [40, 42–44].
The recent ATA guidelines classify nodules into 5 risk groups based on US results [1]. However, the current AACE guidelines suggest a more practical, 3-tier risk classification: low risk, intermediate risk and high risk thyroid lesions, based on their US characteristics [13].
In patients with thyroid nodules and low TSH who have undergone thyroid scintigraphy, ultrasound is useful to check for concordance of the nodule and hyperfunctioning area on the scan, which do not need FNA and to evaluate other nonfunctional or intermediate nodules, which may require FNA based on sonographic criteria [1].