Diagnosis and management of Intratyroid Ectopic Thymus

Intrathyroidal ectopic thymus (IET) is a rare benign condition caused by the aberrant thymic migration during embryogenesis. It is usually incidentally diagnosed as a thyroid nodule. Objective: To report the intrathyroidal location of ectopic thymic tissue and to describe the ultrasound findings in children. Patients and Method: Retrospective descriptive review of the medical charts and thyroid ultrasound studies of children with nodular images in the thyroid gland, in a third level national pediatric hospital, from January 2010 to August 2017. Solid hypoecogenic intrathyroid lesions with multiple linear tracts or hyperechogenic points that did not change their characteristics during follow-up were considered intrathyroidal thymos. The ultrasound follow-up was performed every 4-6 months. The ultrasound characteristics of the lesions (location, laterality, size and shape), the indication of the ultrasound scan and the follow-up time were analyzed. Results: Of 147 patients with thyroid nodules, we identified 12 children with lesions suggestive of an IET (8.1%). The mean age at diagnosis was 3.9 years (range 0-8). It was an incidental finding in all cases. Imaging findings were unilateral in eight patients and bilateral in four patients. All lesions were located in the mid and/or posterior portion of the gland. We adopted a watch-and-wait approach with ultrasound follow-up (mean 2.2 years; range 0.83-4) in all patients except in a 7-year-old boy who presented uncertain findings and underwent surgery, confirming IET in the pathological study. Conclusions: Thymic inclusions in the thyroid gland are a rare but increasingly frequent finding, possibly related to the increased use of ultrasound studies. Pediatricians and radiologists should be aware of this entity to differentiate it from other thyroid lesions, avoiding unnecessary studies and/or treatments in these patients.