Mediastinum

Mediastinum

1. Mediastinu
M

2. DEFINITION OF MEDIASTINUM
•It is a partition between the right & left pleural sacs. It includes
all the structures which lie in the intermediate compartments
of the thoracic cavity

3. Position and boundarie:
Position:
Occupies the median portion of the thoracic cavity in children.
In adults, it slightly bulge to the left side
Boundaries:
The sternum and costal cartilages in front
The thoracic vertebra behind
The mediastinal pleura on both sides
The thoracic inlet above
The diaphragm below

4. Left side of mediastinum
Left subclavian a.
Thoracic duct
Aortic arch
Thoracic aorta
Sympathetic trunk
Greater splanchnic n.
Left vagus n.
Left recurrent n.
Phrenic n. and pericardiacophrenic
a.
Root of lung
Pericardium
Esophagus

5. （1）Esophageal upper triangle
（2）Esophageal lower triangle

6. Right side of mediastnum
Superior vena cava
Phrenic n. and
pericardiacophrenic a.
Root of lung
Pericardium
Trachea
Left vagus n.
Arch of azygos v.
Sympathetic trunk
Esophagus
Inferior vena cava

7. DIVISIONS OF MEDIASTINUM

8. DIVISIONS OF MEDIASTINUM
•It is divided by a horizontal plane
extending from sternal angle to lower
border of 4
th
thoracic vertebra into:
1.Superior mediastinum: above the plane
2.Inferior mediastinum: below the plane, it is
subdivided into:
•Anterior mediastinum: in front of
pericardium
•Middle mediastinum: contains heart &
pericardium
•Posterior mediastinum: behind pericardium

9. SUPERIOR MEDIASTINUM
BOUNDARIES:
•Anterior: manubrium sterni
•Posterior: Upper 4 thoracic vertebrae
•Superior: Plane of thoracic inlet
•Inferior: Horizontal plane
•On each side: Pleura

10. Location:
From inlet of thorax to plane extending from level of sternal angle
anteriorly to lower border of T4 vertebra posteriorly
Contents of superior mediastinumContents of superior mediastinum
4 layers
From anterior to posterior
1- Thymus
2- Veins
3- Arteries
4- Esophageal layer
Nerves in Superior mediastinum :
•Left and right phrenic nerves
•Left and right vagus nerves
•Left recurrent nerve
•Superficial cardiac plexus
•Deep cardiac plexus

11. Thymus
Source of T lymphocytes
Large part lies between the sternum and trachea
Two unequal lateral lobes and one pyramidal lobe
In fetus and infant, it is large
Continue to grow until puberty but is gradually
reduced and replaced by the connective tissue after
mid adult life

13. Veins
Three veins
 Left brachiocephalic v.
 Right brachiocephalic v.
 Superior vena cava

14. BRACHIOCEPHALIC:
•FORMATION: by union of internal jugular & subclavian vein
(behind medial end of clavicle)
•END: Both veins unite to form S.V.C.
•
RIGHT VEIN:
oshorter & has a vertical course,
orelated laterally to right phrenic nerve & right pleura & lung,
oits tributaries in thorax:
•right 1
st
posterior intercostal vein,
•right internal thoracic vein,
•right lymphatic duct

15. LEFT VEIN:
olonger & has an oblique course,
orelated anteriorly to manubrium & thymus gland, &
posteriorly to branches of arch of aorta,
oTributaries in thorax:
•left 1
st
posterior intercostal vein,
•left superior intercostal vein,
•left internal thoracic vein,
•thoracic duct

16. SUPERIOR VENA CAVA:
•FORMATION: by union of brachiocephalic veins, behind lower
border of right 1
st
costal cartilage
•END: opens into right atrium behind right 3
rd
costal cartilage
•TRIBUTARIES: azygos vein

17. Aortic arch and its
branches
ORIGIN: continuation of ascending aorta, opposite upper
border of right 2nd costal cartilage
COURSE & RELATIONS: ascends upward backward & to the left
(behind manubrium & in front of trachea) then curves
backward (to the left of trachea) then finally curves downward
TERMINATION: continues as descending aorta, opposite lower
border of T4

18. BRANCHES OF ARCH OF
AORTA:
BRACHIOCEPHALIC:
•It ascends upward & to the
right (behind left
brachiocephalic vein & in front
of trachea).
•It divides into right common
carotid & right subclavian
arteries (behind right
sternoclavicular joint)

19. 1.LEFT COMMON CAROTID: ascends
upward & to the left (to the left side
of brachiocephalic artery) & enters
the neck (behind left
sternoclavicular joint)
2.LEFT SUBCLAVIAN: ascends upward
(behind left common carotid artery,
in front of esophagus, to the left side
of trachea), arches over apex of left
lung to enter neck

20. Bounded by:
ophrenic n.
oleft vagus n.
oleft pulmonary a.
Contents:
oarterial ligament ,
oleft recurrent n.
osuperficial cardiac
plexuses
Ductus arteriosus triangle

21. is the arterial duct in fetal life,
but is closes to form the ligament after birth.
It connects the origin of left pulmonary artery with the
aortic arch.
Arterial ligament

22. Trachea
Esophagus
Thoracic duct
Esophagus layer

23. TRACHEA
•RELATIONS:
•Anterior: arch of aorta, brachiocephalic & left
common carotid arteries
•Posterior: left recurrent laryngeal nerve,
esophagus
•Right: right vagus nerve
•Left: arch of aorta, left subclavian artery
•NERVE SUPPLY: sympathetic trunks & vagus

24. ESOPHAGUS
•RELATIONS: (in superior mediastinum)
1.Anterior: left recurrent laryngeal nerve, trachea, left
subclavian artery
2.Posterior: thoracic vertebrae
3.Right: right pleura & lung
•RELATIONS: (in posterior mediastinum)
1.Anterior: pericardium, separating it from left atrium
2.Posterior: thoracic duct, descending aorta, azygos vein
3.Right: right pleura & lung
4.Left: descending aorta, left pleura & lung
•NERVE SUPPLY: as trachea
•ARTERIAL SUPPLY: descending aorta
•VENOUS DRAINAGE: azygos & hemiazygos

25. THORACIC DUCT
ORIGIN: from upper end of cysterna chyli (opposite L1 & L2)
COURSE: passes through aortic opening of diaphragm, ascends
in posterior mediastinum (behind esophagus) & in superior
mediastinum (to the left of esophagus) to enter root of neck
END: in left brachiocephalic vein
RELATIONS: ( in posterior mediastinum)
1.Anterior: esophagus
2.Posterior: thoracic vertebrae
3.Right: azygos vein
4.Left: descending aorta

26. THORACIC DUCT
TRIBUTARIES:
oIt drains lymph from both sides of the body below the
diaphragm through cysterna chili
oIt drains lymph from left half of the body above diaphragm
through:
1.Left jugular lymph trunk: drains left side of head & neck
2.Left subclavian lymph trunk: drains left upper limb
3.Left bronchomediastinal lymph trunk: drains left side of
thorax

27. Contents:
Anterior mediastinum
Middle mediastinum
Posterior mediastinum
Inferior mediastinum

28. oThis is a narrow space between the sternum and
pericardium.
oContents:
•the remains of the lower part of thymus,
•the internal thoracic vessels and their branches,
•a part of anterior mediastinal lymph nodes
•some loose connective tissue.
Anterior mediastinum

29. •CONTENTS:
1.Pericardium & heart
2.Arteries: ascending aorta, pulmonary trunk
3.Veins: lower half of superior vena cava, terminations of
inferior vena cava & pulmonary veins
4.Nerves: phrenic
5.Lymph nodes
MIDDLE MEDIASTINUM

30. Fibrous pericardium: A strong outer layer which is
constituted by tough fibrous tissue.
Serous pericardium: A thin inner layer which is
transparent sac. It can be divided into two layers:
oParietal layer: It lines the fibrous pericardium.
oVisceral layer (epicardium): It is closely applied to the heart
and is often called epicardium.
Pericardium

31. Blood vessels in the pericardium:
Pulmonary trunk
Ascending aorta
Superior vena cava
Inferior vena cava
Pulmonary veins

32. Transverse sinus of the pericardium
Oblique sinus of the pericardium
Anteroinferior sinus of the pericardium
Sinuses of pericardium

33. Anteroinferior sinus:
oLies between the anterior and inferior walls of pericardium.
oIts position is lower and close to the anterior wall of thorax.
oThe excessive pericardial fluid may be accumulated in the sinus in
pericarditis, therefore this site is for pericardiocentesis.

34. Oblique sinus:
oLies between the left atrium,
between the right and left
pulmonary veins as the enter
left atrium.
oHere the pericardial pus often
accumulates.

35. Transverse sinus:
oLies transerversely between
the ascending aorta and
pulmonary trunk anteriorly
and superior vena cava and
left atrium posteriorly.
oThe ascending aorta and the
pulmonary trunk can be
clamped by way of the
transverse sinus of
pericardium to block the
blood stream temporarily in
heart operation.