2. Mediastinum
The mediastinum is a broad central partition that
separates the two laterally placed pleural cavities.
It extends:
from the sternum to the bodies of the vertebrae;
and
from the superior thoracic aperture to the
diaphragm
It contains the thymus gland, the pericardial sac,
the heart, the trachea, and the major arteries and
veins.
It also serves as a passageway for structures such as
the esophagus, thoracic duct, and various
components of the nervous system as they traverse
the thorax on their way to the abdomen.
3. DIVISIONS OF MEDIASTINUM
A transverse plane extending from
the sternal angle (the junction
between the manubriumand the
body of the sternum) to the
intervertebral disc between vertebrae
TIV and TV separates the
mediastinum into:
Superior mediastinum
Inferior mediastinum, which is
further partitioned into:
Anterior
Middle
Posterior mediastinum by the
pericardial sac
4.
5. CONTD……
MODIFICATION OF THIS TRADITIONAL
CLASSIFICATION WAS EXCLUSION OF THE
SUPERIOR COMPARTMENT SINCE IT
CONTAINS STRUCTURES THAT FOR THE
MOST PART CONTINUOUS WITH THE
COMPARTMENTS BELOW; THUS ITS
SEPARATION SERVES LITTLE DIAGNOSTIC
PURPOSE
6. According to Heitzman classification, the normal
mediastinum can be divided into following six
anatomic regions…………………
1. THORACIC INLET
2. THE ANTERIOR MEDIASTINUM
3. THE SUPRA-AORTIC AREA
4. THE INFRA-AORTIC AREA
5. THE SUPRA-AZYGOS AREA
6. THE INFRA-AZYGOS AREA
7. THORACIC INLET
(cervicomediastinal continuum)
Represents the junction b/w structures at the base of
the neck and those of the thorax
It parallels the 1st rib
Thus higher posteriorly than anteriorly
8. Boundary of thoracic inlet
Anteriorly : upper border of manubrium sterni
Posteriorly : superior surface of the body of 1st thoracic
vertebra
On each side : 1st rib with its cartilage
The plane of the inlet is directed downwards and
forwards with an obliquity of about 45 degrees
The anterior part of the inlet lies 3.7 cm below the
posterior part
11. CERVICOTHORACIC SIGN
an opacity on a PA chest radiograph that is effaced on
its superior aspect and that projects at or below the
level of clavicle must be situated anteriorly, whereas
one that projects above the clavicles is retrotracheal
and posteriorly situated
13. STRUCTURES OCCUPYING THORACIC INLET
FROM FRONT TO BACK
1. THE PORTION OF THYMUS GLAND
2. RIGHT AND LEFT BRACHIOCEPHALIC VEIN
3.THE COMMON CAROTID ARTERIES
4. THE TRACHEA
5. THE ESOPHAGUS
6. RECURRENT LARYNGEAL NERVES
7. LOWER TRUNK OF BRACHIAL PLEXUS
8. VAGUS AND PHRENIC NERVE
9. THORACIC DUCT
14.
15. ANTERIOR MEDIASTINAL AREA
Bounded anteriorly by the sternum and posteriorly by
pericardium, aorta and brachiocephalic vessels
It is narrowest anteriorly where pleura of right and left
upper lobes converge to form anterior junctional
line
It broadens postero-superiorly in an apex-down-triangular
configuration to form anterior
mediastinal triangle
Compartment contains thymus gland, branches of
internal mamary artery and vein, lymphnodes,the
inferior sternopericardial ligamnet and fatty tissue
16.
17. Thymus gland
Roughly a bi-lobed structure
DEVELOPMENT- bilateral 3rd pharyngeal pouches
EVOLUTION- largest at birth or during infancy
increases slightly during 1st decade of
life and decrease thereafter
Normal weight- 5 – 50 gm
18. Radiology of thymus gland
On conventional chest radiograph it is consistently
visible only in infants and young children……then after
2-3 yrs of age it becomes an inconstant feature
Three radiographic signs aid identification of normal
thymus gland
1. THYMIC NOTCH SIGN
2. SAIL SIGN
3. THYMIC WAVE SIGN
19. Radiology of thymus gland
Sail sign
SAIL SIGN-present
only in 5% of infants
related to the presence of a
triangular opacity of thymic
tissue that projects to the left
or right
20. Thymus radiology
Thymus wave sign
THYMUS WAVE SIGN-Seen
as an undulating or
rippled contour of thymus
border caused by anterior rib
indentation
21. Thymus radiology
THYMUS NOTCH
SIGN-An
indentation of
thymus contour at the
junction of heart and
thymus
22. Anterior junction anatomy
The pleura at the anteromedial portions of the rt and lt
lungs contact the mediastinum in the retrosternal area
to form anterior junction line which defines superior
and inferior recesses
Superior recess – in retro manubrium…typically
marginate a V-Shaped area, the anterior mediastinal
triangle
Shifting of superior recess towards rt indicates rt lower
lobe collapse and vice-e-versa is also true
25. Contd…………
Anterior junctional line is actually a septum the
thickness of which ranging from 1 to more than 3 mm
extending from upper rt to lower lt behind the
sternum from the apex of sup recess upto apex of
inferior recess
Inferior recess – inferiorly the anteromedial portions
of rt and lt lung are farther separated by heart and
mediastinal fat forming a inverted V-shaped area
known as inferior recess
26. SUPRA AORTIC AREA
On the left side of the mediastinum
Extending from aortic arch to thoracic
inlet behind the anterior mediastinum
Structures are –
1. left subclavian artery
2. left wall of trachea
3. left superior intercostal vein
4. mediastinal fat
Most of these structures are in middle
mediastinum except left sup intercostal
vein which is situated in post
mediastinum
27. Retrosternal stripe, parasternal stripe, cardiac incisura
On a true lateral radiograph of the chest when lung is
excluded from the retrosternal space by mediastinal
fat, a vertical retrosternal opacity is often seen known
as retrosternal stripe
The lung can also contact upper 2/3rd of anterior chest
wall thus outlining the parasternal areas and creating
parasternal stripe…..particularly prominent when
the ant surface of lung is lobulated
28.
29. Contd………….
On the left side as the sternum is followed inferiorly
the lung is normally excluded from anteromedial chest
wall by cardiac apex, epicardial fat pad or both..this
deficiency is known as cardiac incisura
Sometimes subclavian arteries cause superior and
posterior indentation and innominate veins cause
inferior and anterior indentation….these are known as
vascular incisura
30. Contd………
Left subclavian artery arises from aorta behind the left
common carotid artery and passes upward lateral to
the trachea in contact with left mediastinal pleura
forming an interface with superomedial left upper lobe
thus can be identified on a PA radiograph as an arcuate
opacity concave laterally
33. Aortic nipple
Left sup intercostal vein has three parts– aortic nipple,
paraspinal portion and retroaortic part
Aortic nipple consists of a rounded protruberance
adjacent to aortic arch that is created by vein seen end
on as it passes anteriorly adjacent to the aortic arch
before entering the left brachicephalic vein
35. Applied anatomy
Seen in 1-10% patients
Normally upto 4.5 mm diameter
Dialatation occurs in-
supine position
Muller maneuvre
systemic venous hypertension
36. Dilated left sup intercostal vein c/b collateral blood flow from
left brachiocephalic vein into azygos and hemi azygos vein
37. Posterior Junction Line
Seen above the level of the azygos vein and aorta and that is
formed by the apposition of the lungs posterior to the
esophagus.
usually extend from third to fifth thoracic vertebrae.
posterior junction line can be seen above the suprasternal
notch and lies almost vertical, whereas the anterior
junction line deviates to the left
38.
39. CT scan shows the posterior junction line (arrow), which
is formed by the interface between the lungs posterior
to the mediastinum and consists of four pleural layers
40. Posteroanterior chest radiograph shows a mass (arrow)
obliterating the posterior junction line. Note that the mass
extends above the level of the clavicle and has a well-demarcated
outline due to the interface with adjacent lung (arrowhead
41. Vascular pedicle
On frontal chest radiography the vascular pedicle
extends from thoracic inlet to top of the heart
On the right side its boundary is formed by right
brachiocephalic vein above and SVC below
The left boundary is formed by left subclavian artery
above and aortic arch below
Right side of pedicle is entirely venous and left side is
purely arterial
42. Measurement of the width of
vascular pedicle
On PA chest radiography from the point at which the SVC
crosses the right main bronchus to the point at which the
left subclavian artery arises from the aortic arch
Normal range- 38-58 mm
Correlation b/w azygos vein width and total blood volume
was poor although correlation with right atrial pressure is
stronger
Extravascular causes of widening of mediastinal silhouette
( aortic trauma or extravasation of blood or saline infusion)
resulted in widening of mediastinal vascular pedicle
44. Infra aortic area
On the left side extends from the aortic arch above to
the diaphragm below and from the anterior
mediastinal space in front to paravertebral region
behind
Contains-
left ventricle
left atrial appendeges
left pulmonary artery
aortic arch
45. Aorto-pulmonary window
A space b/w arch of aorta and left pulmonary artery
Medial boundary – ductus ligament
Lateral boundary – mediastinal pleura
Contents-
fat
left recurrent laryngeal nerve
lymph nodes
46. The lateral border of aorto-pulmonary
window is
normally concave or straight
A lateral convexity should
suggest a mediastinal
abnormality most commonly
lymphadenopathy
Although it may occsionally
be a normal variant caused by
accumulation of fat
47. Supra azygos area
The supra-azygos area is that portion of the right side
of the mediastinum that extends cephalad from azygos
arch to thoracic inlet separated from infra azygos area
by azygos vein and arch
Contents-
tracheal interfaces
azygos and hemiazygos veins
48. Azygos and hemiazygos vein
Originates as an extension of right ascending lumbar
vein or right subcostal vein
In the thorax it is situated in front, to the right or
rarely to the left of the eighth thoracic vertebrae
There it is joined by hemiazygos vein at the level of T8
0r T9
It finally inserts at the back of the superior vana cava
49. Tracheal interfaces
Contact of the right lung in the supra azygos area with
the right lateral wall of the trachea creates a thin stripe
on PA chest designated as rt paratracheal stripe
Normal width of this stripe is 4 mm
More than 5 mm occurs in –
paratracheal lymph node enlargement
mediastinal haemorrage
pleural disease
thickening of tracheal wall
50. Contd………….
Since the left subclavian artery and contiguous
mediastinal fat usually relate to the left border of
trachea, a left paratracheal stripe is seldom seen
Posterior tracheal stripe is a vertically oriented opacity
formed by posterior wall of trachea where it comes in
contact with the right upper lobe parenchyma
51. Azygos arch
At the level of aortic arch the azygos vein consists of
three parts-
1. post / paraoesophageal
2. middle / retrotracheal
3. ant / right tracheo-bronchial angle
Depending upon the distension of the vessel and depth
of the supra azygos and infra-azygos recesses the vein
may be identified on a lateral x-ray as a retro tracheal
elongated opacity as it passes over the right main
bronchus
53. Contd…………
Measurement of ant portion is important in some
diseases-
A. portal hypertension
B. svc obstruction
C. systemic venous hypertension
The only segment that is visible on conventional
radiography is its entry point to the SVC seen as a
slightly flattened elliptical opacity
Normal range is 3-7 mm
55. AZYGOESOPHAGEAL RECESS
The azygos vein ascends in the posterior mediastinum
in relation to the right side or front of the vertebral
column.
The azygoesophageal recess is formed by contact of
right lower lobe with the esophagus and the ascending
portion of the azygos vein.
The recess is frequently identified on well-penetrated
PA radiographs as an interface that extends from the
diaphragm below to the level of azygos arch above.
56. Contact b/w the right lung and the esophagus (straight arrow ) and azygos vein (curved
arrow)
57. HEART
In a frontal chest radiograph the position of heart in
relation to the midline of the thorax depends largely
on the patient’s build.
In asthenic individuals the heart shadow is almost in
the midline only projecting slightly to the left
In those of stockier built it lies a little more to the left
side.
59. Contd……………
In normal subjects the transverse diameter of the heart
measured on standard PA radiographs is usually in the
range of 11.5 – 15.5 cm.
It is measured from chest radiography by calculating
cardio-thoracic ratio.
A cardio-thoracic ratio of 50% is widely accepted as the
upper limit of normal