Primary Tumors of Mediastinum The mediastinum is an anatomic division of the thorax extending from the diaphragm to the thoracic inlet. Mediastinal disorders present as a number of clinical features. Many cases are asymptomatic, and the disorder is identified on routine chest radiographs. Most patients have clinical features related to local involvement of adjacent structures, tumor secretory factors, or immunologic factors. Anatomy of Mediastinum Borders: Superior: the thoracic inlet Inferior: the diaphragm Anterior: the sternum Posterior: the vertebral column Lateral: the parietal pleura Right mediastinal view Left mediastinal view Components of Mediastinal Compartments Anterior Visceral (middle) Paravertebral (posterior) Thymus Pericardium/heart Sympathetic chain Internal thoracic vessels Great vessels Proximal intercostal nerve, artery, and vein Internal thoracic lymph nodes Trachea Posterior paraesophageal lymph nodes Prevascular lymph nodes Proximal right and left mainstem Intercostal lymph nodes Fat and connective tissue Esophagus Phrenic nerve Thoracic duct Proximal azygos vein Paratracheal and subcarinal lymph nodes (levels 2, 4, and 7) Pleuropericardial lymph nodes Fat and connective tissue I. Anterior Mediastinal Masses Differential Diagnosis of a Mass Lesion in the Anterior Mediastinal Compartment. Neoplastic Thyroid Substernal goiter Ectopic thyroid tissue Thymus Thymic hyperplasia Thymoma Thymic carcinoma Thymic carcinoid Thymic cysts Teratoma Mature teratoma Immature teratoma Lymphoma THYMIC TUMORS Thymic Masses. Thymic hyperplasia