Radiologists divide the mediastinum into 3 compartments. The most popular classification is Felson’s division of the thorax into the following 3 compartments:

• Anterior: Everything from the sternum to the posterior aspect of the heart and great vessels.
• Middle: The compartment posterior to the heart and great vessels, to a line drawn 1 cm posterior to the anterior edge of the thoracic vertebrae.
• Posterior: The space behind the posterior limit of the middle mediastinum.
This approach is very useful in classifying mediastinal masses (please refer to Diagnostic Medical Imaging Chapter or to examples of mediastinal masses to follow).