Prevalence and sonographic features of ectopic thyroidal thymus in children: A retrospective analysis

Purpose: To assess the prevalence of ectopic thyroidal thymus tissue detected by sonography (US) in children and to analyze the US features.

Methods: We retrospectively reviewed images of 216 children who had undergone a thyroid or neck US examination from February 2015 to June 2015. Lesions within or adjacent to the thyroid gland that showed echopatterns consistent with thymic tissue were diagnosed as ectopic thyroidal thymus tissue. Lesions were reviewed according to their side, location, level, size, shape, echo pattern, internal content, and vascularization.

Results: A total of 216 children (119 girls, 97 boys) with a mean ± SD age of 8.6 ± 5.2 years were enrolled the study.Thirty children (13girls, 17 boys) (13.9%) had 35 lesions compatible with ectopic thyroidal thymus tissue.Nine children had intrathyroidal (4.2%) and 21 children had extrathyroidal (9.7%) ectopic thymus tissue.The mean ± SD ages of the children with and without ectopic thyroidal thymus tissue were 6.0 ± 3.6 years and 9.1 ± 5.2 years, respectively (P = .002). Twenty-five of the lesions were extrathyroidal and 10 were intrathyroidal. All extrathyroidal and most (8/9) intrathyroidal ectopic thymuses had fusiform shape with well demarcated contours. Ectopic thymuses were located either in the midportion (n = 23) or lower portion of the neck (n = 12). Both extrathyroidal and intrathyroidal ectopic thymuses showed typical hypoechoic (n = 22/25, n = 9/10, respectively) or hyperechoic (n = 3/25, n = 1/10, respectively) echo patterns with internal linear and punctate echoes.

Conclusions: Ectopic thyroidal thymic tissue is common in children. Radiologists should be vigilant about the unique US features of ectopic thyroidal thymus, including a hypo- and hyper-echoic echo pattern with multiple linear and punctate echoes, a fusiform shape, well-demarcated contours, and middle or low-lying location to differentiate it from other neck or thyroid lesions.