The term “mediastinal” refers to the mediastinum, which is the central compartment of the chest cavity. This anatomical space is a tightly packed region situated between the two lungs. The mediastinum acts as a protective container, housing some of the body’s most vital organs. It is surrounded by loose connective tissue that allows for some movement as the organs within it operate.
Where the Mediastinum Is Located
The mediastinum occupies the middle area of the chest, extending vertically from the neck opening down to the diaphragm. It is physically contained on both the left and right sides by the pleural sacs, the membranes that surround the lungs. This positioning means the space runs down the center of the thoracic cavity, separating the two lung fields.
The space is bordered in front by the sternum, or breastbone. In the back, the mediastinum is limited by the vertebral column, or the spine. The vertical limits begin at the superior thoracic aperture, the opening at the top of the rib cage, and terminate at the diaphragm.
Key Structures Housed Within the Mediastinum
The mediastinum is densely populated with organs and vessels, giving it immense functional importance. The most prominent structure is the heart, which is centrally located and encased within the pericardium. Surrounding the heart are the roots of the great vessels, the large arteries and veins that connect directly to the heart chambers.
The major structures housed within this space include:
- The ascending aorta and aortic arch, which carry oxygenated blood away from the heart.
- The superior and inferior vena cava, which return deoxygenated blood.
- The trachea (windpipe) and the esophagus (food passage).
- The thymus gland, a lymphoid organ important for the immune system, particularly during childhood.
- Numerous lymph nodes, which filter lymph fluid from the chest area.
- Important nerves, such as the phrenic and vagus nerves, which regulate functions like breathing and heart rate.
How the Mediastinum Is Anatomically Divided
For medical and surgical purposes, the extensive mediastinal space is conceptually divided into separate compartments. The initial division separates the space into the superior and inferior mediastinum, using the transverse thoracic plane. This imaginary horizontal plane extends from the sternal angle in the front to the lower border of the fourth thoracic vertebra (T4) in the back.
The inferior mediastinum, which lies below this line and above the diaphragm, is further subdivided into three smaller regions. These three areas are designated as the anterior, middle, and posterior mediastinum. This segmentation is based on their relationship to the pericardium, the sac surrounding the heart.
The anterior mediastinum is the smallest compartment, situated in front of the pericardium and behind the sternum. The middle mediastinum is defined by the contents of the pericardial sac, primarily the heart and attached major blood vessels. The posterior mediastinum is the space located behind the heart and pericardium, lying just in front of the vertebral column.
Clinical Significance of the Mediastinum
The tightly confined nature of the mediastinum means that any abnormal growth or inflammation can quickly become serious. The most frequent clinical issue encountered is a mediastinal mass, such as a tumor, cyst, or enlarged lymph node. The specific location of the mass within the anterior, middle, or posterior compartment often helps narrow the diagnosis.
For instance, masses in the anterior mediastinum are often thymomas (tumors of the thymus gland) or lymphomas. These masses can exert a significant effect on nearby structures, known as “mass effect.” This compression can affect the trachea, leading to difficulty breathing, or press on the esophagus, causing trouble swallowing.
Mass effect can also cause compression of large blood vessels, such as the superior vena cava, leading to swelling in the face and neck. Beyond masses, the mediastinum can be affected by mediastinitis, a severe infection of the loose connective tissue in the space. Because the mediastinum communicates with the neck and abdomen, an infection can spread rapidly and become life-threatening if not managed immediately.