Ectopic intrathyroidal thymus in children: Prevalence, imaging findings and evolution

The aim of this study was to evaluate the ultrasound (US) features of intrathyroidal ectopic thymus (IET) and demonstrate the alterations after follow-up. This study included 36 lesions of 32 patients (mean age 95 +/- 58 months) diagnosed with IET. The patients underwent follow-up US examination at least 22-months without a medication or surgical intervention. A total of 36 IETs with an incidence of 0.91% were detected among 3914 thyroid ultrasound (US) examinations. The mean of anteroposterior (ap), transverse (tr), and craniocaudal (cc) diameters in the initial US examinations were 3.1 +/- 1.19 mm, 4.89 +/- 1.86 mm, and 6.45 +/- 3.92 mm respectively. All of the lesions were well-demarcated, hypoechoic to the thyroid gland, and contained uniformly distributed punctate echogenic foci. Follow-up US examinations were performed after 684 +/- 85 days. The alterations between the initial and follow-up diameters for ap and cc direction were not statistically significant. However, a significant difference (p=0.007) was found for transverse diameters and the IETs were found to be smaller at follow-up US than in the initial US. Most of the IETs were located in the left lobe (64%), middle portion (83%), and extended to a border of thyroid gland (69%) and nonspherical in shape (89%). The descriptive findings of IETs are uniform distribution of punctate echogenic foci, absence of a rim, and the presence of vessels traversing through the lesion without parenchymal displacement. Given our findings, healthcare professionals should be aware of the diagnosis of IET. Patients with an IET could be safely managed with follow-up US and any surgical treatment would not be required.