Surgical pathology of the thymus and mediastinum

The thymus is an anterior mediastinal lymphoid organ important for immunological self-tolerance that comprises epithelial, lymphocytic, histiocytic and stromal elements with characteristic histological arrangements. Its complex embryological development means that dysgenesis and embryological remnants may be seen and rarely lead to sequelae such as tumours. Thymic biopsy or thymectomy may be performed for diagnostic reasons, although thymectomy is more commonly performed as a treatment, usually for myaesthenia gravis or tumours. The major categories of thymic pathology include cysts, hyperplasia, thymomas, haematopoietic neoplasms, primary and secondary carcinomas, neuroendocrine tumours, germ cell tumours and soft tissue tumours.