Sonographic findings in ectopic cervical thymus in an infant.

We present the case of a 28-day-old boy with ectopic thymic tissue in the neck. Sonography showed a well-delineated, homogeneous lesion in the left submandibular region that was isoechoic relative to the mediastinal thymus. The lesion had angular margins and lacked a mass effect despite its large size (3 x 2 cm). On power Doppler imaging, arteries with an intermediate-impedance flow pattern were seen entering the lesion from the inferior and lateral margins. On both T1- and T2-weighted MR images, the lesion was isointense relative to the mediastinal thymus and had higher and lower signal intensity than muscle and fat, respectively. A sonographically guided needle biopsy confirmed the diagnosis of ectopic thymus.