Chapter 24

• • Most mediastinal abnormalities are benign and asymptomatic.
• • Division into anterior, superior, middle, and posterior “compartments” facilitates differential diagnosis.
• • More than 60% of lesions in adults are in the anterior-superior mediastinum, whereas more than 60% in children are in the posterior mediastinum.
• • Of masses, 75% in adults and 50% in children are benign.
• • The most common malignant masses of the anterior-superior mediastinum are thymoma, Hodgkin’s disease (HD), non-Hodgkin’s lymphoma (NHL), and germ cell tumors.
• • Neurinomas are the most frequent tumor in the posterior mediastinum and are often recognizable by their classic dumbbell-shaped contour

The finding of an abnormality on chest radiograph or chest computed tomography (CT) most often prompts consideration of diseases of the mediastinum. Findings may be incidental on a radiograph obtained as part of the evaluation of an unrelated clinical issue (eg, suspected pneumonia) or may be recognized on a study obtained to evaluate a specific complaint, symptom, or sign directly referable to potential mediastinal pathology (eg, swallowing difficulty) or after chest trauma (eg, risk of dissection of the thoracic aorta). When present, symptoms are related either to the primary disease process or to associated compressive effects on regional anatomy. Thus, a symptom or sign referable to a particular organ system may not be indicative of primary disease in that system. For example, dysphagia may result from either esophageal pathology or an extrinsic compressing mass.

Although there are no reliable estimates of prevalence, abnormalities of structures within the mediastinum are varied and common. Many abnormalities, such as courses or dilatations of otherwise normal blood vessels, are benign structural variants, which are of no pathological significance. Many nonmalignant lesions occur including pericardial or bronchogenic cysts, aneurysmic dilatations of the aorta and great vessels, benign tumors, and substernal goiters. Such lesions are generally, but not always, asymptomatic. Malignant lesions may be either primary or metastatic, and are equally likely to be symptomatic or asymptomatic. Symptomatic lesions are most often malignant. Thymoma, germ cell tumors, lymphoma, and neurinoma are the most common tumors of the mediastinum.

Anatomically, the mediastinum is the region of the body bounded by the thoracic inlet superiorly, the diaphragm inferiorly, the sternum anteriorly, the vertebral column posteriorly, and the pleura bilaterally (Figure 24–1). Core elements of the respiratory, digestive, and cardiovascular systems are located in this central area as are elements of the neurological, lymphatic, and endocrine systems.

###### Figure 24–1.

Basic anatomy of the mediastinum. A: Anterior view. B: Lateral view. C: Mediastinal divisions.

Separation of the mediastinum into anterior, superior, middle, and posterior subdivisions, although not arbitrary, is somewhat misleading in that there are no clear boundaries that separate ...

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