The term mediastinal means “pertaining to the mediastinum,” a central, mobile compartment located within the chest cavity. This anatomical space resides between the two lungs and the pleural sacs that surround them. It is a region packed with numerous structures that pass between the neck, the thorax, and the abdomen, making it a major thoroughfare for bodily systems. Understanding its location and contents is key to appreciating its significance in human health.
Anatomical Location and Boundaries
The mediastinum occupies the central portion of the thoracic cavity, extending vertically from the thoracic inlet down to the diaphragm. The diaphragm separates the chest from the abdomen and forms the inferior boundary. The front boundary is the sternum (breastbone), and the posterior limit is set by the twelve thoracic vertebrae. Laterally, the compartment is tightly enclosed by the medial surfaces of the pleural sacs, which house the lungs. This arrangement means the mediastinum is a relatively confined space, which has significant implications if structures within it begin to swell or enlarge.
Internal Subdivisions
The central mediastinal space is systematically divided into distinct regions for anatomical description and clinical reference. The primary division is created by an imaginary transverse thoracic plane. This plane passes horizontally from the sternal angle to the intervertebral disc between the fourth and fifth thoracic vertebrae (T4/T5). This division separates the space into the superior mediastinum (above the plane) and the inferior mediastinum (below the plane). The inferior section is further partitioned into three smaller compartments relative to the pericardium, the heart’s protective sac. The anterior mediastinum is the small space in front of the pericardium and behind the sternum. The middle mediastinum is defined by the pericardium and its contents. The posterior mediastinum is the space located behind the heart and in front of the vertebral column.
Key Structures Housed Within
The mediastinum is densely packed with many important organs, vessels, and nerves. The middle mediastinum contains the heart and the roots of the great vessels, including the ascending aorta and the superior and inferior vena cava. The trachea (windpipe) runs through the superior mediastinum and then splits into the main bronchi, providing the primary airway for respiration. Posterior to the trachea is the esophagus, the muscular tube that transports food to the stomach. The area also contains the thymus gland, involved in immune function, located primarily in the superior and anterior compartments. Major nerves like the phrenic nerve, which controls the diaphragm, and the vagus nerve, which influences heart rate and digestion, travel vertically through this central region.
Common Conditions Affecting the Mediastinum
Because the mediastinum is a confined space containing vital structures, even minor swelling can lead to serious health issues. One of the most common pathologies is the development of mediastinal masses or tumors. These growths are often classified based on the compartment they arise in, with anterior masses frequently including lymphoma or thymoma, a tumor of the thymus gland. An infection of the connective tissue within this space is known as mediastinitis, often resulting from a tear in the esophagus or a complication following heart surgery. Doctors also look for mediastinal widening on a chest X-ray, a potentially life-threatening sign where the central shadow appears broader than normal. This widening can indicate a traumatic aortic rupture or an aortic dissection, requiring immediate medical intervention.