involvement of various tumors: Anterior mediastinum: substernal thyroid goiters, lymphoma, thymoma, and teratoma. Middle mediastinum: lymphadenopathy, metastatic disease such as from small cell carcinoma from the lung. Posterior mediastinum: Neurogenic tumors, either from the nerve sheath (mostly benign) or elsewhere (mostly malignant). Mediastinitis is inflammation of the tissues in the mediastinum, usually bacterial and due to rupture of organs in the mediastinum. As the infection can progress very quickly, this is a serious condition. Pneumomediastinum is the presence of air in the mediastinum, which in some cases can lead to pneumothorax, pneumoperitoneum, and pneumopericardium if left untreated. However, that does not always occur and sometimes those conditions are actually the cause, not the result, of pneumomediastinum. These conditions frequently accompany Boerhaave syndrome, or spontaneous esophageal rupture. Widening Widened mediastinum/mediastinal widening is where the mediastinum has a width greater than 6 cm on an upright PA chest X-ray or 8 cm on supine AP chest film. A widened mediastinum can be indicative of several pathologies: aortic aneurysm aortic dissection aortic unfolding aortic rupture hilar lymphadenopathy anthrax inhalation - a widened mediastinum was found in 7 of the first 10 victims infected by anthrax (Bacillus anthracis) in 2001. esophageal rupture - presents usually with pneumomediastinum and pleural effusion. It is diagnosed with water-soluble swallowed contrast. mediastinal mass mediastinitis cardiac tamponade pericardial effusion thoracic vertebrae fractures in trauma patients. See also Mediastinum testis (unrelated structure in the scrotum) Mediastinal germ cell tumor Mediastinitis Mediastinal tumor List of anatomy mnemonics#Mediastinum References External links – "Divisions of the mediastinum." – "The anatomical divisions of the inferior mediastinum." – "Subdivisions of the Thoracic Cavity" Thoracic cavity