Background: There is a rare possibility that during fetal life a small part of the thymus may malmigrate during its descend and remain as a part of the thyroid gland. Though it does not pose any threat to a patient, it is often mistaken for a malignant tumor and is a cause of surgical intervention. The purpose of this study is to present our experience and to create a list of characteristic features of the thymic tissue in the thyroid gland.
Methods: We present a group of 63 children (34 boys, 29 girls) aged 5-16 years old with no thyroid gland disorders. All findings were accidental and occured during standard thyroid examinations. To our knowledge, this is the first paper with such a large group of patients. In each of them a small (3-15 mm) focal change was found which was diagnosed as intrathyroidal thymic tissue. We adopted following features that make the diagnosis of the thymus tissue in the thyroid gland more probable: the location in lower and central part of the thyroid gland near the parathyroid glands; an irregular shape usually with less than 1 cm in diameter; reduction of echogenicity with hiperechogenic focuses; no central and low peripheral blood flow or no flow at all; similarity to the echogenicity of the nearby thymus.
Results: In 4 cases biopsy confirmed our diagnosis and in 2 cases we had a post-surgery confirmation. Other children have been observed, some for over 5 years.
Conclusions: When diagnosing small focal thyroid changes in children ectopic thymus tissue should be considered a possibility.
