Ectopic intrathyroidal thymus misdiagnosed as a thyroid nodule: sonographic appearance.

An 11-year-old boy under suppression therapy for a solitary thyroid nodule was referred for sonographic examination. The diagnosis had been made at another institution, based only on sonography without cytopathologic verification. A small fusiform lesion, which was homogeneously hypoechoic with diffuse bright internal echoes, was demonstrated in the right lower pole of the thyroid. A normal elongated thymus with a cervical component was then found connected to the thyroid with an accessory lobe, which was embedded in the lower thyroid pole mimicking a solitary nodule. We discuss the developmental abnormalities of the thymus and their clinical significance in childhood with a brief review of the literature.