Persistent cervical thymus with a small cyst in a newborn infant.

A boy, aged 1 month, who showed a tumour mass in the right neck, is presented. Operation disclosed that the tumour was a cervical thymus with a small cyst. The cervical thymus degenerated gradually into hypoplasia or thymic cyst due to the abnormal descent of the thymus. It is rare that cervical thymus and/or thymic cyst is detected before the age of one year.