Médiastin

The médiastin is the area of the rib cage located between the two Poumon S containing the Cœur, the esophagus, the Trachée and both Bronche S stocks. Pass also large lymphatic blood-vessels and , as well as nerves. In short cut, it is about the contents of the rib cage when the lungs are removed.

The adjective referring is médiastinal to it. It is divided, by convention, in:

médiastin posterior, in particular containing the esophagus and the downward Aorta;
médiastin average, containing the higher air routes: Trachea and its division (careens);
médiastin former containing the heart, the ascending aorta, the pulmonary arteries and the higher Vena cava.

Total exploration is made by it mainly thanks to the scanner and the Imagerie by magnetic resonance.

Anatomical limits

The médiastin is limited

Ahead, by the posterior face of the Sternum, of the former segments of the coast S and the intercostaux muscles,
Behind, by the body of each dorsal Vertèbre and of the former face of the posterior segments of the coasts.
In top, the médiastin communicates with the cervical area,
In bottom, the muscle diaphragm form the floor of the cavity.
Outwards, the médiastin is limited by the visceral Plèvre of each lung, bored by the pulmonary hiles.

The posterior médiastin

The thoracic channel

The left lymphatic conduit

The left lymphatic conduit is a large lymphatic conduit which drain the Lymphe lower extremities, Abdomen, left side of the Thorax and upper limb left.

It is born from the cistern of the chyle of Pecquet (on the level of the abdomen) and walks on in front of the rachis while crossing the diaphragm with the Aorte to traverse the average médiastin on the right this one. It finally will be thrown in the left confluence jugulo-under-keyboard after having described a stick.

The lymphatic conduit right

The lymphatic conduit right is a trunk, from 1 to 2 cm length, which drains the lymph of the right thorax, of the upper limb right, the Cou and the head.

This conduit is thrown finally to the posterior face of the confluence right jugulo-under-keyboard.

The esophagus

The esophagus is a flexible muscular tube of approximately 25 cm length. It is born from the Pharynx with the level from 6th with 7th Vertèbre S cervical and brings together in the cardia Estomac on the level of 10th with 11th thoracic vertebrae.

The downward aorta and its branches

The aorta describes a short ascending part (leave ascendens aortae) at its exit of the left Ventricule of the Cœur, then an aortic arc (arcus aortae) for finally redirecting in direction the abdomen: the downward aorta (leave descendens aortae) .

the thoracic downward aorta is the principal artery of the posterior médiastin. It gives rise to multiple parietal branches. In particular:

the posterior arteries intercostales which reach intercostaux spaces of 3rd with 11th coasts and distribute several branches towards the walls of the trunk, marrow spinale and Tégument S correspondents.
the artery subcostale passes under the 12th coast.
the higher phrenic arteries which gain the diaphragm.

But also with smaller visceral branches: Branches bronchial, œsophagiens, médiastinaux and péricardiaques.

The average médiastin

The trachea

The Trachée is a curved tube of approximately 11 cm starting on the same level as the esophagus (6th with 7th cervical vertebra) and stopping on the level of the junction trachéale on the level of 4th with 5th thoracic vertebra.

The hull

The hull corresponds to a cartilagineuse projection in with the junction trachéale in form of Y to back separating air flow into two and giving rise to the bronchi stocks right and left.

The pulmonary pedicle

The pedicle of a body is the whole of the vessels which enter this body. For a lung, it is composed of the pulmonary vein lower, another higher, of a pulmonary artery as of a principal bronchus (stock).

The bronchi stocks

The principal bronchi stocks or bronchi result from the subdivision of the trachea. The bronchus right stock is shorter, broader (for example, a subject having badly ingurgity a small food will have a greater probability of seeing this foreign body passing in the bronchus right stock because of its larger diameter with respect to the left bronchus stock) and prolongs the trachea vertically (with a variable angle of approximately 20°) whereas the left bronchus stock is longer, narrower and deviated horizontally of the trachea of an angle of approximately 35° with 40°.

Pulmonary arteries

The pulmonary arteries left and right move respectively towards the Poumon S right and left. The two arteries are divided into ramification parallel to the bronchial tree before returning in the pulmonary Hile.

Pulmonary veins

There are 4 pulmonary veins, those throwing all in the left atrium of the heart. One distinguishes:

the right higher pulmonary vein: this one drains the oxygenated blood of the higher pulmonary lobe and means of the right lung.
the right lower pulmonary vein: it drains the blood of the lower lobe of the right lung.
the left higher pulmonary vein: it drains the blood of the higher lobe (Culmen and Lingula) of the left lung.
the left lower pulmonary vein: it drains the blood of the lower lobe of the left lung.

The higher pulmonary veins are former to the bronchi and the pulmonary arteries; the lower pulmonary veins are posterior with the bronchi.

The blood drainage towards the pulmonary veins is done via veins lobulaires and intersegmentaires (each one bearing the name of the pulmonary segment which they serve)

The aortic arc

The stick of the large vein azygos

The Grande vein azygos is large vessels located on the right of the thoracic rachis. It directly drains intercostaux spaces of 4th at 12th right coasts. On the level of the 4th thoracic vertebra, it describes a stick to span the bronchus right stock and to reach the higher Vena cava located ahead to throw to it with the vein intercostale higher right-hand side, itself draining intercostaux spaces of 1st at 3rd right coasts.

But the large vein azygos also drains via:

the lower Vein hémi-azygos: 8th with the 12th left intercostaux spaces.
the higher Vein hémi-azygos: 7th with the 4th left intercostaux spaces.

which flow in the large vein azygos on the level of the 8th thoracic vertebra.

the vein intercostale higher left is braided ( connected ) with the higher vein hémi-azygos, it pours there the blood of 1st with the 3rd left intercostaux spaces.

The former médiastin

The heart

The Cœur is a muscular Organe which ensures the Blood circulation. It is posed on the diaphragm and is located against the former wall of the Rib cage, behind of this one. It is located on the left in position médiale (about the middle). It consists of two parts:

the right heart which receives the blood deoxygenized of both venas cava in top and bottom and which expels it in the pulmonary trunk in top.
the left heart which receives the blood oxygenated of the four behind pulmonary veins and dispatches it in the Aorte in top.

The ascending aorta

The ascending aorta leaves the left ventricle of the heart. It gives rise to its base with the coronary arteries which come vasculariser the cardiac fabric. The ascending aorta is a short segment and ends in the horizontalisation of this one.

The pulmonary trunk

The pulmonary trunk leaves the ventricle right of the Cœur and moves to the top and the left (passing in front of the Aorte). This trunk is divided into two pulmonary arteries (a right pulmonary artery and a left pulmonary artery) directing each one towards the outside to join the pulmonary hiles. The right pulmonary artery passes under the aortic arch. The division of the trunk of the pulmonary artery is attached to the aorta by an arterial ligament (remainder of the arterial channel).

The higher vena cava and venous trunks brachiocephalic

The brachiocephalic venous trunks right and left respectively join together the veins subclavians and right and left jugular veins. The venous Tronc brachiocephalic left is longer and narrow that the right TVBC which is more in the prolongation of the higher Vena cava in which they flow.

The thymique cabin

The thymique cabin contains the thymus; at the adulthood, it contains only grease, one speaks then about remainder of the thymus.

Nervous system

At the nervous level one finds the nervous chains sympathetic nerves left and right, the pneumogastric nerves (parasympathetic) left and right and the phrenic nerves (for the diaphragm) left and right.

Exploration of the médiastin

Thoracic radiography

Scanner and IRM

Mediastinoscopy

Pathology

Médiastinite
Tumor médiastinale
Surgery of the médiastin

References

Helga Fritsch, Wolfgang Kühnel, Atlas of pocket of anatomy , Volume II: Internal organs, 3rd edition, edition revised by Helmut Leonhardt. ISBN 2257132521

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