The cyst wall contained abundant adipose tissue intermixed with atrophic thymic tissue composed of lymphoid cells, epithelial cords, and Hassall corpuscles.
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.
The presence of thymic parenchyma, lymphoid tissue, and Hassall corpuscles within the adipose cyst wall is considered to be pathognomonic.
Interestingly, sections from the presumed parathyroid gland turned out to also contain ectopic thymic tissue with distinct cortex, medulla, and Hassall corpuscles
Histology identified Hassall corpuscles, and on that basis, a diagnosis of a thymic cyst was made.
Lobules of thymic tissue containing Hassall corpuscles were seen in the cyst wall.
By the tenth week, adjacent mesenchymal cells destroy the solid cords of the pharyngeal ectoderm, and the remaining epithelium transforms into Hassall corpuscles.
In addition, several nests of cytokeratin-positive epithelial cells that formed Hassall corpuscles were scattered throughout the lesion (Figure 2).
Lymphocyte invasion occurs at 10 weeks of gestation, whereas subsequent endodermal regressions form the Hassall corpuscles.
Moreover, the presence of fibrous septa, Hassall corpuscles, and other characteristics of normal thymic architecture on cell block material confirms an unequivocal diagnosis of ectopic thymus.
Hassall corpuscles of the thymic medulla were evident centrally within lobules.
The latter are recognizable by the presence of Hassall corpuscles and lymphocytes.