[Non-neoplastic lesions of the mediastinum]

The mediastinum is a complex body region of limited space but containing numerous organs of different embryonic origins. A variety of lesions that are difficult to distinguish from each other can occur here. Non-neoplastic lesions of the mediastinum represent important differential diagnostic pitfalls to mediastinal tumors, clinically, radiologically and histopathologically. It is important to bear these lesions in mind and to adequately verify or exclude them before starting further differential diagnostic considerations on mediastinal neoplasms. The most common non-neoplastic lesions in this region include cysts and lymphadenopathies. Mediastinal cysts result from abnormal events in the branching of the tracheobronchial tree, the pharyngeal pouches, the primary intestines, the pleuropericardial membranes and the brain meninges or are complications of inflammatory and hydrostatic processes. The histogenesis of the lining epithelium and the cyst wall structure are decisive for the exact classification. The histopathologically most prevalent patterns of mediastinal lymphadenopathies are those accompanied by increased histiocytes and Castleman's disease. Sclerosis is a non-specific reaction pattern of the mediastinum and can be associated with many processes; therefore, when establishing the diagnosis of sclerosing mediastinitis, several differential diagnoses have to be excluded. Simple thymic hyperplasia can be accompanied by considerable increase in organ size with severe local symptoms, while follicular thymic hyperplasia is often associated with myasthenia gravis and represents the most common findings in non-thymoma thymectomy specimens.