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The mediastinum is central, midline thoracic cavity, which is surrounded anteriorly by the sternum, posteriorly by 12 thoracic vertebrae and laterally by pleural cavity.
The mediastinum is divided into the superior mediastinum and inferior mediastinum.
1. Superior mediastinum
The anterior mediastinum is anterior to the heart and contains remnants of the thymus.
The middle mediastinum contains the heart and great vessels.
The posterior mediastinum contains everything that is below the posterior margin of heart i.e. thoracic aorta, esophagus, thoracic duct, azygos veins, and vagus nerve.
Widened mediastinum is when the diameter is greater than 6 cm on upright chest x-ray or greater than 8cm on supine chest x-ray. Few causes of widened mediastinum are:
Left atrial enlargement
MOST COMMON PATHOLOGY IN MEDIASTINUM