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Mediastinum is the region surrounded by the lungs, chest, pleurae and spine from the back and consists of principal tissues and organs of the chest excluding the lungs. Mediastinum is a division of the thoracic cavity and contains the heart and its vessels, the esophagus, the trachea, the phrenic and cardiac nerves, the thoracic duct, the thymus and the lymph nodes of the central chest.
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Key Terms: Mediastinum, Thoracic, Esophagus, Trachea, Phrenic, Infectious, Anterior, Posterior, Arteries, Veins, Lymphoma
Also Read: What are blood vessels?
Structure of Mediastinum
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For the theoretical study, mediastinum is divided into two parts i.e. superior or upper mediastinum and inferior or lower mediastinum. Lower mediastinum is further subdivided into Anterior, Middle and Posterior mediastinum.
Superior or Upper Mediastinum
Superior and upper mediastinum is bordered between the superior thoracic aperture and thoracic plane. This region contains many organs such as thymus, trachea and esophagus. Also, it consists of arteries like aortic arch, brachiocephalic trunk, left common carotid artery, left subclavian artery along with veins such as thoracic duct or brachiocephalic veins. It is a home to left and right vagus, recurrent laryngeal, cardiac, left and right phrenic nerves.
Inferior or Lower Mediastinum
The inferior mediastinum extends from the inferior border of the superior mediastinum to the diaphragm. It is subdivided into three spaces:
- Anterior mediastinum: The region in front of the pericardium is anterior mediastinum. Thymus is the single organ in this area along with internal thoracic branches and parasternal lymph nodes
- Middle mediastinum: It is bounded by the pericardium, which encloses the heart and origins of the great vessels. The nerves such as phrenic and vagus are present in middle mediastinum.
- Posterior mediastinum: Posterior is the field behind the pericardium which contains single organs i.e. esophagus. Thoracic duct and vagus are other veins and nerves present in posterior.
Structure of Mediastinum
Mediastinum Diseases
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The mediastinum contains many organs, nerves and veins which can be affected by the unhealthy habit of the individual that leads to harmful disease such as cancer, nerve damage, benign tumour, mediastinal mass, lymphoma etc.
Mediastinal Masses
Because of the predilection for certain types of masses to occur in specific mediastinal compartments, it is easiest to separately consider masses occurring in each of the three anatomic regions. However, a fair amount of overlap occurs; that is, many types of mediastinal masses are not exclusively limited to the one compartment where they most frequently appear.
Mediastinal masses are caused by a variety of cysts and tumours, likely caused by patient age and by the location of the mass i.e. anterior, middle and posterior mediastinum. This can result in cough, shortness of breath and many more but masses may be asymptomatic (common in adults) or cause obstructive respiratory symptoms (more likely in children).
Lymphoma
Enlarged Lymph nodes cause pain which are mostly found in the cervical or supraclavicular region. It is considered as a type of cancer. It affects mostly the parts of the lymphatic system which are lymph nodes, thymus gland, spleen and bone marrow. The symptoms the affected person shows are coughing or shortness of breath, fatigue, weight loss, fever and many more. Also, abdominal pain is commonly seen in older people, especially after consuming alcohol. It can be cured completely in its initial stage if proper medication is taken.
Also Read: Endocrine Glands
Things to Remember
- Mediastinum is a large anatomic compartment in the thoracic cavity.
- Lungs is not a part of mediastinum.
- Pericardium is the only barrier in the mediastinum.
- Superior and inferior mediastinum are two subdivisions of mediastinum.
- Inferior mediastinum is further divided into three divisions- anterior, middle and posterior.
- In children, the commonest thymic tumour is lymphoma.
- Coughing or shortness of breath are main symptoms of diseases in mediastinum.
Sample Questions
Ques. Where is the mediastinum located? (2 Marks)
Ans. The mediastinum lies within the thorax and is enclosed on the right and left by pleurae. It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It extends from the sternum in front to the vertebral column behind. The region consists of principal tissues and organs of the chest excluding the lungs.
Ques. What is pericardium? (2 Marks)
Ans. Mediastinum is discussed based on subdivisions which are separated by only a physical barrier known as pericardium. Also, the subdivisions of mediastinum are defined on the term pericardium. The region beyond pericardium is anterior mediastinum whereas behind the pericardium is the region of posterior.
Ques. What are the components in Superior mediastinum? (2 Marks)
Ans. Thymus, Trachea and Esophagus are three organs which are part of Superior mediastinum. On the other hand, the aortic arch, brachiocephalic trunk, left common carotid artery, and left subclavian artery are the arteries of it. The left and right vagus are also considered as components of upper mediastinum.
Ques. The superior mediastinum:
(a) Is bounded inferiorly by the diaphragm.
(b) Is bounded anteriorly by the mesosternum (body of sternum).
(c) Is situated anterior to the upper four thoracic vertebrae.
(d) Contains the vena azygos. (3 Marks)
Ans. Option (c) is the correct answer.
Explanation: The superior mediastinum is bounded posteriorly by the four thoracic vertebrae whereas it is enclosed superiorly and inferiorly by the thoracic inlet and transverse thoracic plane respectively. Moreover, the region starts from the thoracic aperture and ends at the thoracic plane. It's important contents are the oesophagus, trachea, great veins, aortic arch and its branches, the vagus, phrenic and left recurrent laryngeal nerves, the upper part of the thoracic duct and the thymus gland.
Ques. What is mediastinoscopy? (2 Marks)
Ans. Mediastinoscopy is a thoracic surgical procedure performed with the instrument called mediastinoscope to examine the mediastinum for various indications, including diagnostic tissue sampling, mediastinal lymph node biopsy, cancer and tumour. The procedure is most often done to remove lymph nodes when a person has lung cancer. The nodes are examined to help see how far the cancer has spread. This can help determine the best treatment choices for lung cancer.
Ques. At mediastinoscopy:
(a) The aortic arch is seen to reach the level of jugular notch.
(b) The left recurrent laryngeal nerve is seen ascending lateral to the aortic arch.
(c) The left brachiocephalic vein is seen to cross posterior to the left common carotid artery.
(d) The left pulmonary artery is seen to lie above the left main bronchus. (3 Marks)
Ans. (d)
Explanation: During the procedure when the mediastinoscope is inserted, it can cause compression of the innominate artery. This can lead to a decrease in pulse oximeter signal and blood pressure when these are placed in the right upper extremity, as a result of the decreased blood flow to the extremity when the artery is compressed. Compression of the innominate artery can lead to intracerebral hypoperfusion which can in turn lead to cerebral ischemia and stroke. In this procedure, the left pulmonary artery is seen to lie above the left main bronchus.
Ques. What is mediastinitis? (2 Marks)
Ans. Mediastinitis is inflammation of the tissues in the mid-chest, or mediastinum. It can be either acute or chronic. It is considered as a serious disease because the infection can spread rapidly and is generally caused by the bacteria. So, it can be life threatening if not taken care of.
Ques. What is acute mediastinitis? (2 Marks)
Ans. Acute mediastinitis is a rare but a life-threatening condition with high mortality and morbidity. The most common causes of acute mediastinitis are postoperative complications and esophageal perforation. Forceful vomiting may result in esophageal perforation and a leak into the mediastinum can result in acute mediastinitis.
Ques. What are the symptoms of mediastinal masses? (2 Marks)
Ans. Almost one-half of patients with a mediastinal mass have no symptoms, and the mass is first detected on incidentally performed chest imaging. In patients who develop symptoms, the most common are chest pain, cough, and dyspnea. Muscle pain is another common symptom in affected people.
Ques. How can mediastinal masses be detected? (2 Marks)
Ans. In almost all cases, the initial diagnostic test is the posteroanterior and lateral chest radiograph, which generally shows the mass and allows determination of its location within the mediastinum. The mass can be further characterized by a variety of other techniques, but CT is generally the most valuable. The contrast-enhanced CT scan is particularly useful for defining the cross-sectional appearance of the lesion, its density, and its relationship to other structures within the mediastinum.
Ques. What are the causes of mediastinum diseases? (2 Marks)
Ans Mediastinum diseases are caused by the unhealthy activities of the individual such as smoking and drinking alcohol. Secondly, the growing age also affects the health of the person which results in getting caught by the diseases. Thirdly, the malfunction of any component of the mediastinum leads to infection.
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