Sonographic appearance of intrathyroid ectopic thymus in children

The aim of this study is to report the common location of intrathyroid ectopic thymus and describe the corresponding sonographic appearances in children.

We retrospectively reviewed clinical data and neck or thyroid ultrasonography (US) findings in children from January 2003 to May 2010. Intrathyroid lesions showing hypoechogenicity with multiple linear echogenic branching structures or punctate echogenic foci were considered intrathyroid ectopic thymus. US features of the lesions (location, side, size, and shape) and the indication for US were recorded.

A total of 5,414 neck or thyroid US examinations were conducted in 3,195 children. We found 15 lesions that were suspected of being intrathyroid ectopic thymus in 12 patients (0.4%), four boys and eight girls, with a mean age of 6.4 years. The lesions were unilateral in nine patients and bilateral in three patients. All the lesions were located at the mid to lower portion of the thyroid. The long-axis diameter of the lesions ranged from 0.7 to 2.2 cm (mean diameter: 1.5 cm). All lesions had a fusiform shape with well-defined margins.

The possibility of intrathyroid ectopic thymus should be considered when a mid- to low-lying intrathyroid lesion with a fusiform shape with multiple linear or punctate internal echoes is detected on US in children.