Bilateral ectopic cervical thymus presenting as a neck mass: Ultrasound and magnetic resonance imaging.

Ectopic cervical thymus (ECT) is a rare cause of neck mass in the pediatric age group. It is extremely uncommon in infants. Overall more than 100 cases have been reported in the literature, though fewer than 10% involved infants. Furthermore, ECT is usually unilateral and more frequently seen in men than in women. Ultrasound (US) is the preferred initial imaging modality, especially in pediatric neck masses given its wide availability, low cost and lack of radiation exposure. US can show the location, extension, and echotexture of the ECT. Magnetic resonance imaging (MRI) can be performed to verify the diagnosis and confirm communication between the ECT and the mediastinal thymus. Diffusion restriction can aid diagnosis when seen in a neck mass similar to that in the mediastinal thymus. Herein is described a case of bilateral ECT in a 2-month-old boy with associated US and MRI findings.