Mediastinum
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The Mediastinum

"Mediastinum" - medial septum: median region between the two pleural sacs

Boundaries

Superior - superior aperture of thorax = thoracic inlet

Inferior – diaphragm

Anterior – sternum, manubrium & costal cartilages

Posterior – Bodies of thoracic vertebrae

Lateral-mediastinal pleura

 

Subdivisions

are in relation to pericardium:

(Pericardium = closed membranous sac enveloping the heart).

Superior mediastinum - region superior to line connecting sternal angle and T4-T5 disc

Inferior mediastinum - subdivisions:

Anterior mediastinum - anterior to pericardium

Middle mediastinum - pericardium and contents

Posterior mediastinum - posterior to pericardium

 

Contents of mediastinum

heart & great vessels

remnant of thymus (in adults)

distal end of trachea & proximal parts of right and left bronchi

Esophagus

vagus nerves & phrenic nerves

thoracic duct & lymph nodes

fat

 

Superior Mediastinum

Brachiocephalic veins

internal jugular and subclavian veins combine to form brachiocephalics

L & R brachiocephalic vv. combine to form superior vena cava

R. brachiocephalic receives right lymphatic duct (see lymphatics)

L. brachiocephalic receives left superior intercostal v. & thoracic duct (lymphatics)

formed by L & R brachiocephalics and empties into right atrium

also receives Azygous from posterior mediastinum

returns blood from above diaphragm, except lungs, which returns into left atrium

terminal half of superior vena cava is in the middle mediastinum (inside pericardium)

 

 

Aortic arch begins posterior to right half of sternal ang le and passes posterior and to left of trachea and esophagus pushing trachea to right and constricting esophagus

becomes descending aorta at disc between T4 + T5

arches over left bronchus, left pulmonary artery and bifurcation of pulmonary trunk

Brachiocephalic trunk

divides into right common carotid and right subclavian

Left common carotid

Left subclavian artery

 

Nerves

Right vagus nerve

descends between right common carotid and right subclavian a.

gives R. recurrent laryngeal n. that hooks under subclavian a. & ascends to larynx

breaks into right pulmonary, posterior esophageal & anterior cardiac plexi

Left vagus nerve

descends between left common carotid and left subclavian a.

gives off L. recurrent laryngeal n. that hooks under the aorta posterior
to ligamentum arteriosum and ascends between trachea & esophagus to larynx

breaks into left pulmonary, anterior esophageal & posterior cardiac plexi

 

 

Phrenic nerves: traveling inferiorly to diaphragm, between subclavian vv. and aa.

Lymphatics

Thymus: most superficial structure in mediastinum prominent in early childhood but reduced to fatty tissue in adults

R. lymphatic duct empties into R. brachiocephalic v. at subclavian & jugular vv. Union

collects lymph from upper right quadrant of body (half of head and thorax + right arm)

Thoracic duct empties into L. brachiocephalic v. at jugular & subclavian vv. Junction

collects lymph from the rest of the body including abdomen and lower limbs

 

Trachea & esophagus

Trachea begins at larynx and branches at level of sternal angle => not in post. Mediastinum

supported by "C" rings opened posteriorly where they lie against esophagus

Esophagus begins at pharynx and runs to stomach, lies between trachea and vertebrae

constricted behind aortic arch & left bronchus (and also in pharynx & diaphragm)

 

Anterior Mediastinum

Contains fat, lymph nodes (sternal) and vessels, sternopericardial ligaments

In infants and children it may contain part of thymus, in adults only fatty tissue

 

Middle Mediastinum

We will spend a whole lecture on this

 

Posterior Mediastinum

Thoracic aorta

continuation of aortic arch; enters abdomen via aortic hiatus (in diaphragm)

lies against left pleura where it impresses left lung

gives off paired segmental intercostal aa, and unpaired bronchial (lungs), esophageal,pericardial & diaphragmatic branches

Left and right pulmonary arteries

 

Veins

Pulmonary veins

two on both sides: superior and inferior

 

Azygos system

azygous receives right intercostal vv and empties on superior/inferior vena cavae

hemiazygous and accessory hemiazygous receive left intercostal vv. and join azygos

azygous system also receives vertebral venous plexus, mediastinal, esophageal and bronchial vv.

Superior intercostal v. (left) empties directly in L. brachicephalic v.

 

Lymphatics

Thoracic duct

carries lymph from all body except upper left quadrant (right side, diaphragm up)

at level of T5 it deviates left and empties into union of left jugular & subclavian vv.

 

Splanchnic nerves

from sympathetic ganglia (autonomics traveling to abdomen)