Congenital thymic cyst in the neck.

Cervical thymic cysts are rare. Thirty-four cases are reported in the English literature. Persistence of a part of thymopharyngeal duct may lead to the cyst formation in the neck. The majority of the cysts are seen in children under 10 years of age. There is marked variation in the size of the cysts. The majority of them are multilocular and the color of the fluid varies widely. The epithelial lining is variable; the majority of the cysts show stratified squamous epithelium. The characteristic histological features are Hassal's corpuscles, cholesterol crystals and aggregates of lymphocytes. Our patient was a four and a half year old female; she presented with a four month history of a painless swelling in the neck. The multilocular bluish-black cyst excised from the left side of the neck had all the histological features of a thymic cyst. A pre-operative diagnosis of such a cyst can be made only by bearing in mind the possibility of thymic remnants in the neck.