The document describes the anatomy and divisions of the mediastinum. It notes that the mediastinum is the central partition in the chest that contains structures like the heart, great vessels, trachea and esophagus. It divides the mediastinum into superior, anterior, middle and posterior compartments. The anterior mediastinum contains the thymus gland while the middle mediastinum contains the heart and pericardium. Various radiographic signs of mediastinal structures are also described.

1. Dr Fahad Shafi
P.G 1ST Year
Deptt. of Radiodiagnosis

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

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

9. Plane of thoracic inlet

10. Thoracic inlet boundary

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

12. CERVICOTHORACIC SIGN ON CHEST X-RAY

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

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

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

23. Radiology of anterior junction

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

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

31. Left subclavian artery

32. Mri demonstrate normal course of left subclavian artery

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

34. Course of left superior intercostal 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

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

43. MEASUREMENT OF 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

52. AZYGOS ARCH

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

54. Infra azygos area
 Content –
1. azygo oesophageal recess
2. heart

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.

58. HEART CHAMBERS IN RELATION TO MEDIASTINUM

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

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