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The mediastinum is centrally located in the thoracic cavity. It extends from the thoracic inlet to the diaphragm and from the sternum to thoracic spine, and it is demarcated by the pleural cavities laterally. Clinically, the mediastinum is divided into anterior, middle, and posterior compartments.

The anterior compartment is defined as the space posterior to the sternum and anterior to the heart and brachiocephalic vessels. It extends from the thoracic inlet to the diaphragm and it contains the thymus, fat, loose connective tissue, and lymph nodes. The boundary of the middle, or visceral, compartment extends from the anterior border of pericardium to the anterior border of the vertebral bodies. Contained within this space are the transverse aorta, the brachiocephalic vessels, the vena cavae, the hilar pulmonary vessels, the trachea and main bronchi, the esophagus, and the lymph nodes. The posterior compartment is not truly a mediastinal space. It is between the anterior border of the vertebral bodies and the posterior curvature of the ribs. The azygos vein, sympathetic chain, vagus nerve, thoracic duct, descending aorta, and the lymph nodes are located within the posterior compartment.

Primary mediastinal tumors represent a heterogenous group of neoplastic, congenital, and inflammatory conditions. Although the heart, trachea, and esophagus lie within the mediastinum, tumors that originate in these structures are outside the scope of this chapter. Table 65-1 summarizes the common neoplasms broken down into the different compartments within the mediastinum. Generally, the most common causes of an anterior mediastinal mass are thymomas, teratomas, thyroid disease, and lymphomas (so called “3T+1L”). Masses of the middle mediastinum include bronchogenic, foregut or pericardial cysts, lymphadenopathy, and inflammatory granulomas. Tumors that are located in the posterior mediastinum are often neurogenic tumors.

TABLE 65-1:

Differential Diagnosis of a Mediastinal Mass by Anatomic Locationa

The likelihood of malignancy is influenced by the tumor location, patient’s age, and the presence or absence of symptoms.1 By tumor location, the anterior mediastinum is associated with the highest incidence of malignancy (54%), followed by the posterior mediastinum (26%), and finally the middle mediastinum (20%).2 With regards to the patient’s age, neurogenic tumors present most commonly during the first decade of life, lymphomas and germ cell tumors (GCTs) during the second through fourth decades, and thymomas, thyroid masses, and lymphomas during the fifth decade and beyond.3 Finally, approximately 80% of asymptomatic patients with mediastinal tumors have benign lesions, whereas 60% of the lesions present in symptomatic patients are malignant.2

The most common symptoms at presentation are cough, chest pain, sensation of chest ...

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