The mediastinum is the region between the pleural sacs. It is separated into three compartments (Table 289-1). The anterior mediastinum extends from the sternum anteriorly to the pericardium and brachiocephalic vessels posteriorly. It contains the thymus gland, the anterior mediastinal lymph nodes, and the internal mammary arteries and veins. The middle mediastinum lies between the anterior and posterior mediastina and contains the heart; the ascending and transverse arches of the aorta; the venae cavae; the brachiocephalic arteries and veins; the phrenic nerves; the trachea, the main bronchi, and their contiguous lymph nodes; and the pulmonary arteries and veins. The posterior mediastinum is bounded by the pericardium and trachea anteriorly and the vertebral column posteriorly. It contains the descending thoracic aorta, the esophagus, the thoracic duct, the azygos and hemiazygos veins, and the posterior group of mediastinal lymph nodes.
TABLE 289-1The Three Compartments of the Mediastinum |Favorite Table|Download (.pdf) TABLE 289-1 The Three Compartments of the Mediastinum
| ||Anterior Compartment ||Middle Compartment ||Posterior Compartment |
|Anatomical boundaries ||Manubrium and sternum anteriorly, pericardium, aorta, and brachiocephalic vessels posteriorly ||Anterior mediastinum anteriorly, posterior mediastinum posteriorly ||Pericardium and trachea anteriorly; vertebral column posteriorly |
|Contents ||Thymus gland, anterior mediastinal lymph nodes, internal mammary arteries, and veins ||Pericardium, heart, ascending and transverse arch of aorta, superior and inferior vena cavae, brachiocephalic arteries and veins, phrenic nerves, trachea, and main bronchi and their contiguous lymph nodes, pulmonary arteries, and veins ||Descending thoracic aorta, esophagus, thoracic duct, azygos and hemiazygos veins, sympathetic chains, and the posterior group of mediastinal lymph nodes |
|Common abnormalities ||Thymoma, lymphomas, teratomatous neoplasms, thyroid masses, parathyroid masses, mesenchymal tumors, giant lymph node hyperplasia, hernia through foramen of Morgagni ||Metastatic lymph node enlargement, granulomatous lymph node enlargement, pleuropericardial cysts, bronchogenic cysts, masses of vascular origin ||Neurogenic tumors, meningocele, meningomyelocele, gastroenteric cysts, esophageal diverticula, hernia through foramen of Bochdalek, extramedullary hematopoiesis |
The first step in evaluating a mediastinal mass is to place it in one of the three mediastinal compartments, since each has different characteristic lesions (Table 289-1).
Computed tomography (CT) scanning is the most valuable imaging technique for evaluating mediastinal masses and is the only imaging technique that should be done in most instances. Barium studies of the gastrointestinal tract are indicated in many patients with posterior mediastinal lesions, because hernias, diverticula, and achalasia are readily diagnosed in this manner. An iodine-131 scan can efficiently establish the diagnosis of intrathoracic goiter.
A definite diagnosis can be obtained with mediastinoscopy or anterior mediastinotomy in many patients with masses in the anterior or middle mediastinal compartments. A diagnosis can be established without thoracotomy via percutaneous fine-needle aspiration biopsy or endoscopic transesophageal or endobronchial ultrasound-guided biopsy of mediastinal masses in most cases. An alternative way to establish the diagnosis is video-assisted thoracoscopy. In many cases, the diagnosis can be established ...