1. Imaging Anatomy of the Mediastinum
Dr. Flip Otto
Dept. of Radiology
Universitas Academic Hospital

2. Outline Mediastinal devisions Content of mediastinum
Mediastinal contours on PA chest radiograph
Cross sectional anatomy of mediastinum
Mediastinal lines and stripes on conventional radiography and CT correlation
Mediastinal spaces
Mediastinal lymphnodes

3. Mediastinal devisions
Devisions used to describe location of pathological processes:
Superior mediastinum:
Above line from lower border T4 to sternal angle
Anterior mediastinum:
Between anterior part of heart and sternum
Middle mediastinum:
Occupied by heart and its vessels
Posterior mediastinum:
Between posterior part of heart and thoracic spine

4. Mediastinal contents

5. Mediastinal contents Superior mediastinum: Anterior mediastinum:
Aortic arch and branches
Brachiocephalic veins and SVC
Trachea
Oesophagus
Thoracic duct
Lymph nodes
Nerves
Anterior mediastinum:
Thymus
Mammary vessels

6. Mediastinal contents cont.
Posterior mediastinum:
Descending aorta
Oesophagus
Azygos venous system
Thoracic duct
Para-aortic, oesophageal and paraspinal nodes
Middle mediastinum
Heart and pericardium
Nerves
Lymph nodes
Great vessels

7. Mediastinal contours on PA chest radiograph

8. Mediastinal contours on PA chest radiograph (from above downwards)
Left side:
Composite shadows of left subclavian vessels (artery lower and actually forms contour)
Aortic knuckle formed by posterior part of arch
Small “nipple” where left superior intercostal vein crosses aorta
Aortopulmonary window
Left main pulmonary artery
Left ventricle
Right side :
Right brachiocephalic vein
SVC
Right atrium (right heart border)
Terminal part of IVC just medial to cardiophrenic angle

9. Cross sectional Anatomy on CT T3 level4 3 5 6 1 7 2
1-trachea 2-oesophagus 3-right braciocephalic vein
4-left brachiocephalic vein 5-right brachiocephalic artery
6-left common carotid artery 7-left subclavian artery

10. Cross sectional Anatomy on CT T4 level5 1 2 3
1-trachea 2-aortic arch 3-oesophagus
4-superior vena cava 5-arch of azygos vein

11. Cross sectional Anatomy on CT T5 level3 1 7 2 11 6 8 5 10 12 4 9
1-main pulmonary trunk 2-right pulmonary artery 3-ascending aorta
4-descending aorta 5-left main bronchus 6-right main bronchus
7-superior vena cava 8-oesophagus 9-azygos vein
10-azygoesophageal recess 11-left superior pulmonary vein
12-left descending lower-lobe artery

12. Cross sectional Anatomy on CT T6 level2 3 1 4 6 5 7
1-aortic root 2-right ventricular outflow tract 3-right atrial appendage
4-left atrium 5-descending aorta 6-oesophagus
7-azygos vein

13. Cross sectional Anatomy on CT T8 level2 1 5 4 3 7 6 8
1-right atrium 2-right ventricle 3-left atrium
4-left ventricle 5-left ventricular outflow tract and aortic valve
6-descending aorta 7-oesophagus 8-azygos vein

14. Cross sectional Anatomy on CT T10 level3 4 2 1 5
1-descending aorta 2-fundus of stomach 3-inferior vena cava
4-oesophago-gastric junction 5-spleen

15. Mediastinal lines and stripes- Correlation between plain chest radiography and CT
Anterior junction line
Posterior junction line
Stripes:
Right paratracheal stripe
Left paratracheal stripe
Posterior tracheal stripe
Posterior wall of bronchus intermedius
Interfaces:
Right paraspinal line
Left paraspinal line
Aortic-pulmonary stripe
Azygo-oesophageal recess

16. Anterior junction line

17. Anterior junction line
Apposition of visceral and parietal pleura of anteromedial aspects of the lungs with intervening mediastinal fat
Oblique line crossing superior two thirds of sternum from upper right to lower left
Increased mediastinal fat or thymus in younger patients lead to appearance as a stripe
Superior and inferior V-shaped recesses
Seen on 24.5%-57% of frontal chest radiographs
Obliteration or abnormal convexity of line suggests anterior mediastinal disease such as thyroid masses, lymphadenopathy, neoplasms, thymic masses or lipomatosis
Volume loss or hyperinflation of surrounding lung may displace the line

18. Abnormal anterior junction line
Volume loss in right lung with rightward displacement of anterior junction line following a right middle lobectomy

19. Posterior junction line

20. Posterior junction line
Apposition of visceral and parietal pleura of posteromedial portion of lungs posterior to oesophagus and anterior to T3-T5
Straight or leftward convex line projecting through trachea
May appear as stripe with intervening posterior mediastinal fat
Superior and inferior V-shaped recesses
Seen on 32% of PA chest radiographs
Abnormal bulging or convexity suggests posterior mediastinal abnormality such as oesophageal masses, lymphadenopathy, aortic disease or neurogenic tumours.
Volume loss or hyperinflation of surrounding lung may displace the line

21. Right paratracheal stripe

22. Right paratracheal stripe
Formed by visceral and parietal pleura of right upper lobe in contact with right lateral border of trachea and intervening mediastinal fat.
Maximum normal thickness of 4mm.
From level of clavicles superiorly to right tracheobronchial angle at the level of the azygos arch inferiorly.
Seen on 97% of PA chest radiographs
Widening or abnormal contour may be due to paratracheal lymphadenopathy, thyroid or parathyroid neoplasms, and tracheal carcinoma or stenosis. Pleural disease among most common causes for widening.

23. Abnormal right paratracheal stripe
Widening of right paratracheal stripe caused by a large ectopic parathyroid adenoma. Note diffuse osteopenia from hyperparathyroidism.

24. Left paratracheal stripe

25. Left paratracheal stripe
Formed by contact between left upper lobe and mediastinal fat adjacent to left tracheal wall or wall itself.
Extends from aortic arch superiorly to join with reflection from the left subclavian artery.
Seen on 21%-31% of PA chest radiographs. May be obscured by contact between left lung and left common carotid artery anteriorly or left subclavian artery posteriorly.
Abnormal contour or widening commonly due to pleural effusion, also due to left paratracheal lymphadenopathy, neoplasm or mediastinal haematoma.

26. Abnormal left paratracheal stripe
Widening of left paratracheal stripe with mass effect on the trachea due to large thyroid carcinoma and associated supraclavicular lymphadenopathy

27. Posterior tracheal stripe

28. Posterior tracheal stripe
Vertical stripe seen on lateral chest radiograph formed by air in trachea and right lung outlining posterior tracheal wall and intervening soft tissues.
Up to 2.5mm in thickness
When posterior trachea in contact with anterior oesphageal wall may measure up to 5.5mm.
Anterior border of retrotracheal space (Raider or retrotracheal triangle) with spine posteriorly and aortic arch inferiorly forming remaining borders.
Most common abnormality in retrotracheal space is developmental anomalies of the aortic arch
Abnormal thickening also caused by acquired vascular lesion, oesophageal lesions, lymphatic malformations, mediastinitis and post-traumatic haematomas.

29. Abnormal posterior tracheal stripe
Widening of the posterior tracheal stripe due to dilated esophagus in a patient with achalasia.

30. Posterior wall of bronchus intermedius

31. Posterior wall of bronchus intermedius
Formed when lung within azygoesophageal recess outlines posterior wall of bronchus intermedius which continues to descend 3-4cm after take-off of the right upper lobe bronchus.
Seen on 90%-95% of lateral chest radiographs.
Thin, vertical or slightly oblique stripe projecting through radiolucent area created by left upper lobe bronchus
Normally mm thick
Pulmonary oedema from congestive cardiac failure common cause for band-like thickening
Other causes for thickening include neoplasms and lymphadenopathy

32. Abnormal posterior wall of bronchus intermedius
Diffuse bandlike thickening of the posterior wall of the bronchus intermedius in a patient with pulmonary oedema.

33. Right paraspinal line

34. Right paraspinal line
Formed by right lung and pleura coming in tangential contact with posterior mediastinal soft tissues
Thin white line enhancing edge of right paraspinal line due to positive Mach band phenomenon
Straight line from T8-T12
Seen on 23% of PA chest radiographs
May be displaced laterally by osteophytes or prominent mediastinal fat
Abnormal contour or displacement may suggest posterior mediastinal abnormality such as mediastinal haematoma, a mass or extramedullary haematopoiesis.

35. Abnormal right paraspinal line
Abnormal bulge in right paraspinal line inferiorly due to mediastinal hematoma from multiple right sided transverse process fractures and an associated hemothorax.

36. Left paraspinal line

37. Left paraspinal line
Formed by tangential contact of left lung and pleura with posterior mediastinal fat, paraspinal muscles and adjacent soft tissues.
Extends vertically from aortic arch to diaphragm medial to lateral wall of descending thoracic aorta, but may lie lateral along lower intrathoracic course of the aorta
Reported on 41% of PA chest radiographs. Seen more frequently than right because aorta promotes tangential contact of lung
Osteophytes, prominent mediastinal fat, tortuosity of descending aorta, mediastinal haematoma, a mass, extramedullary haematopoiesis or oesophageal varices may displace line

38. Abnormal left paraspinal line
Focal lateral bulge in left paraspinal line due to extensive esophageal varices in patient with liver cirrhosis.

39. Aortic-pulmonary stripe

40. Aortic-pulmonary stripe
Represents mediastinal reflection formed by pleura of anterior left lung coming in contact with and tangentially reflecting over mediastinal fat anterolateral to the left pulmonary artery and aortic arch.
Straight to mildly convex crossing laterally over aortic arch and main pulmonary artery.
May be elevated in pneumomediastinum.
Anterior mediastinal disease such as prevascular lymphadenopathy, thyroid or thymic masses may cause increased convexity laterally.

41. Abnormal aortic-pulmonary stripe
Abnormal contour of the aortic-pulmonary stripe due to lymphoma with anterior mediastinal lymphadenopathy within the prevascular space.

42. Azygoesophageal recess

43. Azygoesophageal recess
Important mediastinal interface due to differences in density between mediastinum and posteromedial right lower lobe
Space lying lateral or posterior to oesophagus and anterior to the spine from level of arch of azygos to aortic hiatus inferiorly
Right infra-azygos pleuroesophageal stripe may outline recess when air filled oesophagus and intervening pleura come in contact with right lower lobe
Superioly and middle thirds may show mild leftward convexity. Lower third typically straight edge.
Superior right convexity may be seen in the young, but is abnormal in the elderly.
Abnormal contour may be due to lymphadenopathy, hiatal hernias, bronchopulmonary-foregut malformations, oesophageal neoplasms, pleural abnormalities and cardiomegaly with left atrial enlargement

44. Abnormal azygoesophageal recess
Abnormal contour and right lateral convexity of distal third of azygoesophageal recess due to a large hiatal hernia.

45. Mediastinal spaces Four named spaces surrounding the central airways:
Pretracheal space
Aortopulmonary window
Subcarinal space
Right paratracheal space

46. Aortopulmonary window

47. Aortopulmonary window
Mediastinal space seen as interface on frontal chest radiographs
Lies posterior to aortic-pulmonary stripe
Borders:
Superior: Inferior wall of aortic arch
Inferior: Superior wall of left pulmonary artery
Anterior: Posterior wall of ascending aorta
Posterior: Anterior wall of descending aorta
Medial: Trachea anteriorly, lateral wall of left main bronchus and oesophagus posteriorly
Lateral: Left lung and pleura in contact with aortic arch and extending inferiorly to contact left pulmonary artery – forms interface representing AP window on frontal chest radiographs, normal concave reflection along mediastinal side. Convex contour abnormal.

48. Abnormal aortopulmonary window - causes
May be related to disease of contents: left recurrent laryngeal nerve; left vagus nerve; ligamentum arteriosum; mediastinal fat; lymph nodes; left bronchial arteries
Abnormal convexity may be due to prominent mediastinal fat, lymphadenopathy, bronchial artery aneurysms or nerve sheath tumours
Paralysis of left vocal cord or diaphragm should prompt search for disease in AP window
Disease of structures forming borders of AO window e.g. aortic aneurysms can also cause abnormal appearance

49. Abnormal aortopulmonary window
Abnormal bulge in AP window due to significant soft tissue mass within AP window and subcarinal space compatible with metastatic lymphadenopathy in a patient with bronchogenic carcinoma. Also widened right paratracheal stripe due to lymphadenopathy and left lower lobe consolidation.

50. Mediastinal lymphnodes
American Thoracic Society definitions of regional lymph node stations
X Supraclavicular nodes
2R Right upper paratracheal nodes
2L Left upper paratracheal nodes
4R Right lower paratracheal nodes
4L Left lower paratracheal nodes
5 Aortopulmonary nodes
6 Anterior mediastinal nodes
7 Subcarinal nodes
8 Paraesophageal nodes
9 Right or left pulmonary ligament nodes
10R Right tracheobronchial nodes
10L Left tracheobroncheal nodes
11 Intrapulmonary nodes

51. Conclusion
Traditional frontal and lateral chest radiography remains a valuable tool in the evaluation of chest disease despite increased reliance on CT, therefore familiarity with anatomic basis of mediastinal lines and stripes as seen on radiography imperative.
Knowledge of normal anatomic structures within different mediastinal divisions helps guide formulation of appropriate differential diagnosis

52. References
Butler, P., Mitchell, A.W.M., Ellis, H. (1999). Applied Radiological Anatomy. Cambridge: Cambridge University Press
Ellis, H., Logan, B.M., Dixon, A.K. (2007). Human Sectional Anatomy – Atlas of body sections, CT and MRI images, 3rd ed. London: Hodder Arnold
Gibbs, J.M., Chandrasekhar, C.A., Ferguson, E.C. et al. (2007). Lines and Stripes: Where did they go? – From Conventional Radiography to CT. Radiographics, 27:33-48.
Netter, F.H. (2011). Atlas of Human Anatomy, 5th ed. Philadelphia: Saunders Elsevier
Ryan, S., McNicholas, M., Eustace, S. (2011). Anatomy for diagnostic imaging, 3rd ed. London: Saunders Elsevier