Ectopic intrathyroidal thymus in children: Two case reports and review of the literature

Thymic vestiges remaining at certain locations during embryologic thymic descent may result in ectopic thymus formation. Ectopic thymus most commonly occurs in the cervical area or mediastinum, whereas ectopic intrathyroidal thymic tissue is a rare occurrence. This report describes a 26-month-old male patient and a 52-month-old female patient, both of whom presented with an asymptomatic left intrathyroidal mass. The imaging findings were nonspecific and preoperative fine-needle aspiration (FNA) biopsies were lack, so preoperative diagnosis was difficult. After surgical resection, biopsy showed ectopic intrathyroidal thymic tissue. Differential diagnosis of thyroid nodules or neck masses should include ectopic thymus. Correct diagnosis of ectopic thymus must rely on the histopathologic results, and FNA biopsy may be a feasible way.