Cervical thymic cysts: CT appearance of two cases including a persistent thymopharyngeal duct cyst

The differential diagnosis of cervical cysts in children includes common entities such as branchial cleft cysts, thyroglossal duct cysts, and cystic hygromas. Congenital thymic cysts are uncommon and often misdiagnosed as either branchial cleft cysts or cystic hygromas. However, they may have an appearance on CT that can be characteristic. The course of the descent of embryologic thymic tissue in the neck to the mediastinum indicates the potential site of deposition of an ectopic cervical thymic cyst. In a child, a cystic lesion that has an intimate relationship to the carotid sheath is likely to be a thymic cyst. Of the approximately 100 cases of vestigial cervical thymus or thymic cysts that have been reported in children, only 5 cases of a persistent thymopharyngeal duct cyst have been described [1-5]. In two of these five, the persistent thymopharyngeal duct cyst was demonstrated by CT [1,2]. We report one additional case of a cervical thymic cyst and one case of a persistent thymopharyngeal duct cyst both depicted by CT.