The cervical ectopic thymus is a rare cause of a cervical mass in childhood. It develops secondary to failure of or incomplete descent, implantation or persistence of remnant tissue or failure of involution; resulting in a cervically positioned thymus above the brachiocephalic veins.
It may show regression in size, but residual focal thymic tissue may persist throughout life as an anatomical variant.
The radiological diagnosis is very important to avoid unnecessary biopsy and surgical intervention.