Congenital cysts are usually unilocular, arise from a persistent patent thymopharyngeal duct
, and usually present as a unilocular cystic mass confined to the mediastinum or extending inferiorly within the neck, paralleling the sternocleidomastoid muscle as a dumbbell-shaped left cervicothoracic cystic mass (Fig.
During the 6th week, as the paired thymic buds develop from ventral out-growths, the thymopharyngeal duct forms caudally along the course of migration of the thymus into the mediastinum.
Thymopharyngeal duct cyst: An unusual cause of respiratory compromise.
The congenital theory is based on the hypothesis that cervical thymic cysts develop from the persistence of the thymopharyngeal duct
, while the acquired theory is based on the hypothesis that cervical thymic cysts develop as a result of the degeneration of Hassall corpuscles within remnants of ectopic thymic tissue.
Similar to the thyroglossal duct cysts, when the duct fails to involute, a cyst may occur anywhere along the thymopharyngeal duct
from the angle of the mandible to the upper mediastinum (Figure 6).
Both outgrowths elongate medially and caudally to form the thymopharyngeal ducts