The mediastinum is an essential part of the body located in between the lungs. This area extends from the sternum to the vertebral column, and from the diaphragm to the thoracic inlet. It houses the heart, esophagus, trachea, thymus, and several major blood vessels. The mediastinum provides a conduit for several essential structures in the thorax and is one of the most complex regions in the body.
What is the Mediastinum?
The mediastinum is the central compartment of the thoracic cavity located between the two pleural cavities. It is bordered by the sternum anteriorly, the vertebral column posteriorly, the lungs laterally, the thoracic inlet superiorly, and the diaphragm inferiorly. It is divided into the superior and inferior mediastinum by an imaginary line drawn transversely across the thorax at the level of the sternal angle. The mediastinum is enclosed in a thick layer of connective tissue called the mediastinal pleura.
What structures are located in the Mediastinum?
The mediastinum contains several important structures, including:
- Heart and great vessels
- Trachea
- Esophagus
- Thymus gland
- Lymph nodes and lymphatic vessels
- Nerves and nerve plexuses
- Thoracic duct
- Pericardium
What is the Function of the Mediastinum?
The mediastinum plays a crucial role in the circulation, respiration, and immune system. It is responsible for:
- Encasing and protecting vital organs and structures, such as the heart and great blood vessels.
- Providing an anchoring point for the trachea and bronchi, which allows for normal airway function.
- Facilitating communication between the thoracic and abdominal cavities through the esophagus.
- Housing the thymus gland, which plays a role in the development of the immune system.
- Draining lymph from the thorax through the thoracic duct.
- Providing pathways for nerves and their transmission.
What are the Types of Mediastinum?
The mediastinum is divided into superior and inferior sections for ease of description. The inferior mediastinum contains three subsections:
- Anterior mediastinum: It is located anterior to the pericardium and contains lymph nodes, fat, and connective tissue.
- Middle mediastinum: It contains the pericardium, heart, and great vessels.
- Posterior mediastinum: It is located posterior to the pericardium and contains the esophagus, thoracic aorta, thoracic duct, and azygos venous system.
What is the Superior Mediastinum?
The superior mediastinum is an anatomical space present above the plane of the sternal angle. It is bounded posteriorly by the vertebrae, anteriorly by the manubrium and sternum, and by a transverse plane passing through the sternal angle. Superior mediastinum is often restricted to the area extending from the superior thoracic aperture to the middle of the thorax. It contains the following structures:
- Thymus gland: The superior mediastinum contains thymus gland in infants and children, which eventually becomes replaced by adipose tissue in adulthood.
- Great vessels and blood vessels: The superior mediastinum hosts the superior vena cava and aortic arch, as well as other associated blood vessels.
- Trachea and phrenic nerves: The trachea descends from the larynx and bifurcates at the level of the sternal angle to form the right and left main bronchi. The phrenic nerves travel through the superior mediastinum to innervate the diaphragm.
- Esophagus: The tubular structure that connects the pharynx to the stomach lies at the posterior aspect of the superior mediastinum.
What are the Medical Conditions Related to the Mediastinum?
The mediastinum is the location of many critical structures and can be involved in many medical conditions. Here are a few conditions that can affect the mediastinum:
Mediastinal Tumors:
Mediastinal tumors are growths that occur most commonly inside the mediastinum. These tumors include:
- Thymoma: A mass that arises from thymus gland cells.
- Lymphoma: A cancer that affects lymphocytes in the thymus or lymph nodes in the mediastinum.
- Germ cell tumors: These develop from germ cells located in the testicles or ovary and can spread to the mediastinum.
- Teratoma: A usually benign tumor that can appear at any age and can contain other tissue types such as muscle or bone.
- Neurogenic tumors: These tumors arise from nerve cells in the mediastinum.
Mediastinitis:
Mediastinitis refers to inflammation of the mediastinum and can be caused by infections, autoimmune diseases, or trauma to the chest. Common microbes that can cause mediastinitis include bacteria, viruses, and fungi. Symptoms may include fever, chest pain, cough, and shortness of breath.
Thoracic Aortic Aneurysms (TAA):
Aortic aneurysms are abnormal dilations of the walls of an artery. The thoracic aorta is a common site of aortic aneurysms, and they can cause compression of the mediastinum or the surrounding structures. Symptoms may include chest pain, back pain, and shortness of breath.
Pericarditis:
Pericarditis is inflammation of the pericardium, the fibrous sac surrounding the heart. It can occur due to infectious or non-infectious causes and can lead to chest pain, shortness of breath, and palpitations. Pericarditis can also occur secondary to a variety of diseases, including rheumatic fever or systemic lupus erythematosus, which can cause mediastinal inflammation.
Conclusion
The mediastinum is an anatomically complex region of the thorax that plays a crucial role in the circulation, respiration, and immune system. It is an area filled with essential structures such as the heart and great vessels, lymph nodes, nerves, and other key structures. There are many medical conditions that can affect the mediastinum, ranging from tumors, infections, and autoimmune diseases, to trauma.
Common Questions and Answers
- What is located in the mediastinum?
- The mediastinum contains several essential structures, including the heart, great vessels, lymph nodes, nerves, thymus gland, esophagus, trachea, and bronchi.
- What is the function of the mediastinum?
- The mediastinum plays a crucial role in the circulation, respiration, and immune system. It provides an anchoring point for the trachea and bronchi, facilitates communication between the thoracic and abdominal cavities through the esophagus, and drains lymph from the thorax through the thoracic duct.
- What are some medical conditions that can affect the mediastinum?
- Some conditions that can affect the mediastinum include mediastinal tumors, mediastinitis, thoracic aortic aneurysms, and pericarditis.
- What is the superior mediastinum?
- The superior mediastinum is an anatomical space present above the plane of the sternal angle. It contains structures like thymus gland, great vessels and blood vessels, trachea and phrenic nerves, and the esophagus.
References:
- Naidich DP, Webb WR, Martinez S. Mediastinum In: Computed Tomography and Magnetic Resonance of the Thorax. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2006; 168–243.
- Leong SL, Iyer VR. Mediastinum. [Updated 2021 Mar 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482412/
- Mediastinum – an overview | ScienceDirect Topics.https://www.sciencedirect.com/topics/medicine-and-dentistry/mediastinum