Echogenic foci in thyroid nodules: significance of posterior acoustic artifacts

This study was undertaken to define and evaluate echogenic foci and their posterior acoustic artifacts in thyroid nodules. Whether these findings were indicative of benignity or malignancy was assessed.

Echogenic foci were classified into five types: no posterior artifact, large comet-tail artifact, small comet-tail artifact (≤1.0 mm), and posterior shadowing (subdivided into internal versus peripheral). Nodules were also classified into four parenchymal patterns: hypoechoic, hyperechoic, >50% solid, and cystic. Results were compared with the cytologic or surgical findings.

A total of 704 nodules had echogenic foci; 246 did not. The prevalence of malignancy ranged between 15.4% and 19.5% for all types of foci except large comet-tail artifacts (3.9%). Foci without posterior artifacts had a 21.9% rate of cancer in hypoechoic lesions and 15.8% in hyperechoic lesions. Foci with small comet-tail artifacts had a 27.6% rate of malignancy in hypoechoic nodules. For internal calcifications, no malignant nodules were found in either partially cystic group. Nodules with peripheral calcifications had prevalence rates of 20.0% in cystic nodules and 11.1% in predominately solid nodules. Identification of one additional type of high-risk focus increased the chance of malignancy 1.48 times.

All categories of echogenic foci except those with large comet-tail artifacts are associated with high cancer risk. Identification of large comet-tail artifacts suggests benignity. Nodules with small comet-tail artifacts have a high incidence of malignancy in hypoechoic nodules. With the exception of nodules that have peripheral calcifications, the risk of malignancy is low when echogenic foci are present in partially cystic lesions.