<unk>  is divided into superior and inferior compartments, the latter further subdivided into anterior, middle and posterior compartments.
Anterior
Retrosternal goiter
Thymoma
Germ-cell tumor
Lymphadenopathy (lymphoma)
Middle
Aortic arch aneurysm
Dilated pulmonary artery
Tracheal lesion
Posterior
Esophageal lesions
Hiatal hernia
Descending aortic aneurysm
Paraspinal abscess
Retrosternal goiter
Thymoma
Germ-cell tumor
Lymphadenopathy (lymphoma)
Aortic arch aneurysm
Dilated pulmonary artery
Tracheal lesion
Esophageal lesions
Hiatal hernia
Descending aortic aneurysm
Paraspinal abscess
Widened mediastinum
Neck mass
Chest wall pain
Right atrial enlargement
Pneumomediastinum
Hemoptysis
Tracheostomy obstruction
Paradoxical vocal fold motion