Thyroid Nodules Evaluation with Sonography

Thyroid nodules are common and occur in up to 50% of the adult population; however, less than 7% of thyroid nodules are malignant. US is the most sensitive method for diagnosing intra thyroid lesions. It can depict 2-mm cystic lesions and 3-mm solid intra thyroid lesions. The challenge is differentiating a few malignant nodules from common benign nodules. Despite US's ability to clearly identify nodules, no single US criterion is reliable in differentiating benign ones from malignant thyroid nodules. Even so, many US features may aid in predicting the benign or malignant nature of a given nodule. [1, - 6] Most cystic lesions are benign masses that contain internal debris with a solid component that is hyper echoic relative to the adjacent thyroid tissue. Typically, benign nodules are well defined (96% benign). Lesions demonstrating eggshell calcification and a thin echo lucent halo around the entire lesion are most often benign. Some authors have found that the halo sign is present in 21-33% of thyroid cancers. Typically, malignant nodules are mostly solid and hypo echoic, with irregular margins and, at times, fine punctate calcification in the nodule, particularly in papillary carcinomas. Thyroid cancer has a hypo echoic texture, as compared with that of a normal thyroid gland, because a malignancy contains many cells that lack colloid. Carcinoma is hypo echoic in 68-100% of patients; however, a hypo echoic nodule is more likely to be benign than malignant, because benign nodules are highly prevalent in the general population. Recent research has revealed a correlation between osteopontin messenger RNA expression and the formation of micro calcification seen on US in papillary thyroid carcinomas. [7]Considerable overlap may exist between benign nodules and malignant nodules.