Ectopic Intrathyroidal Thymus in Children: A Long-Term Follow-Up Study

Abstract

Background: Ectopic intrathyroidal thymus has recently been reported in children as a cause of surgery and/or invasive diagnostic procedures when mistaken for a thyroid nodule. Thymus has a unique appearance at ultrasound (US). Methods: We report a follow-up study (mean 34 months, range 6–84) performed by US on 9 children (5 females) with a mean age of 6.3 ± 3.2 years with intrathyroidal thymic inclusions diagnosed by US as ‘incidentalomas’. None has palpable nodules. Results: Intrathyroidal thymic inclusions appeared on US as a hypoechoic area, with regular linear or punctuate internal hyperechoic echoes. The 2 oldest patients (13 and 17 years) showed a regression in both size and hypoechogenicity of thymic inclusions over time – reflecting the normal thymic involution with advancing age. Conclusions: Indeed, the lack of progression seen in our 9 patients over a mean time of 34 months confirmed the substantially benign and self-limited nature of this process. The increasing use of thyroid ultrasonography in children may result in an increased detection of intrathyroidal thymic inclusions – an embryologic anomaly that should be considered in the differential diagnosis of thyroid nodules in children and adolescents.

Intrathyroidal ectopic thymus in children: a sonographic survey

“…In one patient with FNA proven IET, the lesion increased in echogenicity during follow-up and at month 33, the borders of the lesion were less welldefined. Such an increase in echogenicity and borders getting less well-defined have been described during the involution phase [6]. However, our patient was a 5 yearold, which would be too early for pubertal regression of thymic tissue; therefore, it seems such changes might be encountered earlier than previously reported.…”

“…In a female patient with bilateral IET (Patient 13), the lesion on the right was slightly smaller by age 10, whereas the le- 1 Longitudinal x AP x transverse; if only 2 dimensions are given transverse x AP; 2 Respectively; side, craniocaudal location as described in methods, anteroposterior location as described in methods; 3 All lesions were hypoechoic compared to surrounding thyroid, had well defined borders and were identical in sonographic appearance to normal thymus of the patient; 4 Underwent fine-needle aspiration; cytologic diagnosis was IET. The echogenicity of the lesion increased during follow-up; 3 Underwent hemithyroidectomy; pathologic diagnosis was IET; 6 Lost to follow-up. R-right, L-left.…”

“…Besides these seven children, there were 7 children already under follow-up with IET, diagnosed by A.K. using sonographic criteria described in the literature [4][5][6][7]. All 14 children (6 female, 8 male, mean age 6±3.0 range 2-12) with a total of 16 lesions were included in the follow-up phase of the study.…”

“…and followed-up by him until the onset of the study. Based on previous reports in the literature, all intrathyroid lesions showing typical features of multiple punctate and linear branching echogenic structures, identical in appearance to normal thymus of the patient in anterior mediastinum were considered IET [4][5][6][7]. All patients with suspected IET were further evaluated by A.K, who confirmed or refuted the diagnosis.…”

Changes in pediatric thyroid sonograms in or nearby the Kanto region before and after the accident at the Fukushima Daiichi nuclear power plant

“…If the thymus partially remains in the thyroid during this process, an intrathyroidal ectopic thymus is formed. According to one report, among 9 patients with an intrathyroid ectopic thymus (mean age, 6.3) who underwent longterm follow-ups, the ectopic thymus grew smaller over time [20], thus endorsing the findings of our study.…”