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Introduction

Primary lesions of the mediastinum are less common than lesions that secondarily involve the mediastinum. Overall, the majority of masses discovered in the mediastinum will be found to be metastases from a primary lung cancer. Neoplasms that arise primarily in the mediastinum, however, are often encountered in the clinic and are represented by a variety of lesions. This chapter first reviews the anatomy of the mediastinum and then focuses on the benign and malignant neoplasms that arise within each of the anatomic regions of the mediastinum. Covered elsewhere in this textbook (see Chapter 80) are nonneoplastic disorders of the mediastinum that include pneumomediastinum, acute mediastinitis, chronic mediastinitis, and other miscellaneous disorders. Likewise, congenital lesions of the mediastinum, such as bronchogenic, enterogenous, neurogenic, thymic, pericardial, and thoracic duct cysts, are also covered elsewhere (see Chapter 81).

Anatomy of the Mediastinum

The mediastinum comprises an anatomic space located between the thoracic inlet and the diaphragm, and bordered on the left and right sides by the pleural cavities. This central anatomic location houses or borders vital structures of almost every major organ system including the heart and great vessels of the circulatory system, the esophagus, and major airways of the aerodigestive tract, the thymus of the immune system, and important nerves such as the phrenic and vagus nerves. Further, various endocrine organs may project into it, distant malignancies may metastasize to it, and infectious processes can manifest themselves within it.

The mediastinum is compartmentalized based upon the borders of anatomic structures as seen on a lateral chest radiograph (Fig. 82-1). We believe that the most anatomically appropriate and clinically useful model of the mediastinum is the three-compartment model.1 The three-compartment scheme divides the mediastinum into anterior, middle, and posterior compartments. Here, the anterior mediastinum extends from the thoracic inlet superiorly to the diaphragm inferiorly and is bounded anteriorly by the posterior table of the sternum, and posteriorly by the anterior pericardium and the aorta, innominate vein, and brachiocephalic vessels. The content of the anterior compartment includes the thymus, variable amounts of fat and lymphatic tissues, and the internal mammary arteries and veins. The middle compartment of the mediastinum is bounded anteriorly by the pericardium and posteriorly by the pericardium and posterior wall of the trachea, extending only as high as the pericardial reflection. The middle mediastinum contains the heart, pericardium, superior and inferior vena cava, ascending and transverse aorta, trachea and mainstem bronchi, and lymphatic tissues. The posterior mediastinum extends from the thoracic inlet to the diaphragm, and in this “three-compartment scheme,” lies posterior to the posterior pericardium and airway. It includes the descending aorta, thoracic duct, esophagus, vagus nerves, and lymph nodes, as well as structures emerging from the spinal canal such as intercostal nerves.

Figure 82-1

Three-compartment model of the mediastinum. A. Lateral radiograph of the chest. B. Schematic representation of the contents of ...

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