MEDIASTINUM :
Introduction :-
The median septum of the thoracic cavity between the two pleural cavities is known as the mediastinum, or L. middle septum. With the exception of the lungs, it is made up of all the viscera and thoracic cavity structures, such as the esophagus, trachea and major bronchi, aorta, heart and its great blood vessels, mediastinal lymph nodes, etc. The middle section of the thoracic cavity is occupied by the mediastinum. Therefore, in technical terms, it is a wide central partition that divides the two pleural cavities that are positioned laterally. On both sides, the mediastinal pleura covers it.
Boundaries of the Mediastinum :-
Superior Boundary: superior thoracic aperture, often known as the thoracic inlet
bounded by the first pair of ribs, the manubrium of the sternum, and the first thoracic vertebra (T1)
Inferior Boundary: Diaphragm
Anterior Boundary: Ribs’ cartilage between the costal cartilage and the sternum
Posterior boundary: From T1 to T12, the vertebral column .
Lateral Lines of Boundaries: The parietal pleura next to the mediastinum is known as the mediastinal pleura.
Division of the Mediastinum :-
In order to describe and organize the structures, the mediastinum is artificially divided into two parts:
(a) the superior mediastinum and
(b) the inferior mediastinum by an imaginary plane called the transverse thoracic plane that passes through the lower border of the body of the fourth thoracic (T4) vertebra and the intervertebral disc of the T4 and T5 vertebrae posteriorly and the sternal angle anteriorly. The pericardium, which encloses the heart, further divides the inferior mediastinum into three segments.
The term anterior mediastinum refers to the region in front of the pericardium, while posterior mediastinum refers to the region behind it. The middle mediastinum is made up of the pericardium, its contents (the heart, and the roots of its main veins).
(a) Superior mediastinum :-
Location- Above the sternal angle, which is the level of the horizontal plane that runs through the manubrium and sternum’s body and upward to the thoracic inlet.
Boundaries : Anteriorly, there is the Manubrium sterni.
The bodies of the upper four thoracic vertebrae lie posteriorly.
Superior plane: at the upper level of the thoracic opening.
Inferior plane is an imaginary plane that passes posteriorly through the lower edge of the body of the fourth thoracic vertebra and anteriorly through the sternal angle (transverse thoracic plane).
Laterally: the mediastinal pleura on both sides
Content-
1. Arteries : (a) The aortic arch .
(b) The artery in the brain.
(c) The carotid artery on the left.
(d) Artery of the left subclavia.
2. Veins: (a) Brachiocephalic veins on the left and right.
(b) The superior vena cava’s upper portion (SVC).
(c) The superior intercostal vein on the left.
3. Nerves: (a) The left and right phrenic nerves.
(b) The left and right vagus nerves.
(c) Right and left cardiac nerves, as well as sympathetic trunks.
(d) Laryngeal recurrent nerves on the left.
4. Lymphatics and lymphoid organs: (a) lymph nodes.
(b) The thoracic duct .
(c) Thymus.
5. Tubes: (a)Trachea.
(b)Esophagus.
6. Muscles: (a) Sternohyoid.
(b) Sternothyroid.
(c) Longus colli.
(b) Inferior Mediastinum :-
The pericardium, or surrounding heart, further divides the inferior mediastinum into three sections.
Anterior Mediastinum :-
Location: In between the pericardium and the sternum.
Boundaries : The sternum’s body is anterior.
Posterior: Heart enclosed by the pericardium.
The superior mediastinum is divided from the lower mediastinum by the transverse thoracic plane.
Diaphragm is inferior.
Sides: Pleura mediastinalis.
Content : 1. Areolar tissue that is loose.
2. The ligaments known as superior and inferior sternopericardial that extend from the sternum to the pericardium.
3. Four lymph nodes or three.
4. The internal thoracic (mammary) arteries’ mediastinal branches.
5. The lower part of the thymus (in kids).
Middle Mediastinum :-
Location: Centrally located within the thoracic cavity.
Boundaries: The anterior mediastinum is anterior.
Posterior: Mediastinum posterior.
Superior: The mediastinum superior.
Diaphragm is inferior.
Content : 1. The heart
2. The pericardium
3. Arteries : (a) The pulmonary trunk bifurcates into two pulmonary arteries (b) The ascending aorta (c) The pericardiophrenic arteries
4. Veins: (a) Lower portion of the Superior Vena Cava
(b) Azygos vein (terminal portion) (c) The left and right pulmonary veins
5. Nerves: (a) Deep cardiac plexus (b) Phrenic nerves
6. Lymph nodes: (a) Nodes in the tracheobronchial cavity
7. Tubes: (a) Tracheal bifurcation (b) Left and right main bronchi
Posterior Mediastinum :-
Position: In between the spinal column and the pericardium.
Boundaries :- Anterior: pulmonary vessels, tracheal bifurcation, and the pericardium and its Lower eight thoracic vertebral bodies and the intervertebral discs that separate them are located posteriorly.
superior: the transverse thoracic plane that divides the superior and inferior mediastinums.
Lateral: pleura mediastinal
Content: 1. the esophagus
2. The thoracic duct
3. The thoracic aorta descends and its branches
4. nerves of vagus
5. Sympathetic trunks and splanchnic nerves. 6. Azygos hemiazygos and auxiliary hemiazygos vein.
7. Lymph nodes posterior to the mediastinal