Thymic cyst abnormal thymus morphology thymus cyst Thymic cysts are rare mediastinal lesions and are thought to result from the congenital persistence of thymopharyngeal tracts and acquired, progressive cystic degeneration of thymic (Hassall) corpuscles and epithelial reticulum of the thymus; congenital cysts are unilocular, whereas acquired cysts are usually multilocular and result as a consequence of inflammatory processes. thymus cysts presence of one or more fluid-filled spaces lined by epithelium within the thymus MP:0014130 thymic cysts thymic cyst cystic thymus abnormal cyst thymus cyst