1. Dr Fahad ShafiP.G 1ST YearDeptt. of Radiodiagnosis

2. Mediastinum The mediastinum is a broad central partition thatseparates the two laterally placed pleural cavities. It extends: from the sternum to the bodies of the vertebrae;and from the superior thoracic aperture to thediaphragm It contains the thymus gland, the pericardial sac,the heart, the trachea, and the major arteries andveins. It also serves as a passageway for structures such asthe esophagus, thoracic duct, and variouscomponents of the nervous system as they traversethe thorax on their way to the abdomen. 3. DIVISIONS OF MEDIASTINUM A transverse plane extending fromthe sternal angle (the junctionbetween the manubriumand thebody of the sternum) to theintervertebral disc between vertebraeTIV and TV separates themediastinum into: Superior mediastinum Inferior mediastinum, which isfurther partitioned into: Anterior Middle Posterior mediastinum by thepericardial sac 4. CONTD MODIFICATION OF THIS TRADITIONALCLASSIFICATION WAS EXCLUSION OF THESUPERIOR COMPARTMENT SINCE ITCONTAINS STRUCTURES THAT FOR THEMOST PART CONTINUOUS WITH THECOMPARTMENTS BELOW; THUS ITSSEPARATION SERVES LITTLE DIAGNOSTICPURPOSE 5. According to Heitzman classification, the normalmediastinum can be divided into following sixanatomic regions1. THORACIC INLET2. THE ANTERIOR MEDIASTINUM3. THE SUPRA-AORTIC AREA4. THE INFRA-AORTIC AREA5. THE SUPRA-AZYGOS AREA6. THE INFRA-AZYGOS AREA 6. THORACIC INLET(cervicomediastinal continuum) Represents the junction b/w structures at the base ofthe neck and those of the thorax It parallels the 1st rib Thus higher posteriorly than anteriorly 7. Boundary of thoracic inlet Anteriorly : upper border of manubrium sterni Posteriorly : superior surface of the body of 1st thoracicvertebra On each side : 1st rib with its cartilage The plane of the inlet is directed downwards andforwards with an obliquity of about 45 degrees The anterior part of the inlet lies 3.7 cm below theposterior part 8. Plane of thoracic inlet 9. Thoracic inlet boundary 10. CERVICOTHORACIC SIGNan opacity on a PA chest radiograph that is effaced onits superior aspect and that projects at or below thelevel of clavicle must be situated anteriorly, whereasone that projects above the clavicles is retrotrachealand posteriorly situated 11. CERVICOTHORACIC SIGN ON CHEST X-RAY 12. STRUCTURES OCCUPYING THORACIC INLETFROM FRONT TO BACK1. THE PORTION OF THYMUS GLAND2. RIGHT AND LEFT BRACHIOCEPHALIC VEIN3.THE COMMON CAROTID ARTERIES4. THE TRACHEA5. THE ESOPHAGUS6. RECURRENT LARYNGEAL NERVES7. LOWER TRUNK OF BRACHIAL PLEXUS8. VAGUS AND PHRENIC NERVE9. THORACIC DUCT 13. ANTERIOR MEDIASTINAL AREA Bounded anteriorly by the sternum and posteriorly bypericardium, aorta and brachiocephalic vessels It is narrowest anteriorly where pleura of right and leftupper lobes converge to form anterior junctionalline It broadens postero-superiorly in an apex-down-triangularconfiguration to form anteriormediastinal triangle Compartment contains thymus gland, branches ofinternal mamary artery and vein, lymphnodes,theinferior sternopericardial ligamnet and fatty tissue 14. Thymus gland Roughly a bi-lobed structure DEVELOPMENT- bilateral 3rd pharyngeal pouches EVOLUTION- largest at birth or during infancyincreases slightly during 1st decade oflife and decrease thereafter Normal weight- 5 50 gm 15. Radiology of thymus gland On conventional chest radiograph it is consistentlyvisible only in infants and young childrenthen after2-3 yrs of age it becomes an inconstant feature Three radiographic signs aid identification of normalthymus gland1. THYMIC NOTCH SIGN2. SAIL SIGN3. THYMIC WAVE SIGN 16. Radiology of thymus glandSail sign SAIL SIGN-presentonly in 5% of infantsrelated to the presence of atriangular opacity of thymictissue that projects to the leftor right 17. Thymus radiologyThymus wave sign THYMUS WAVE SIGN-Seenas an undulating orrippled contour of thymusborder caused by anterior ribindentation 18. Thymus radiology THYMUS NOTCHSIGN-Anindentation ofthymus contour at thejunction of heart andthymus 19. Anterior junction anatomy The pleura at the anteromedial portions of the rt and ltlungs contact the mediastinum in the retrosternal areato form anterior junction line which defines superiorand inferior recesses Superior recess in retro manubriumtypicallymarginate a V-Shaped area, the anterior mediastinaltriangle Shifting of superior recess towards rt indicates rt lowerlobe collapse and vice-e-versa is also true 20. Radiology of anterior junction 21. Contd Anterior junctional line is actually a septum thethickness of which ranging from 1 to more than 3 mmextending from upper rt to lower lt behind thesternum from the apex of sup recess upto apex ofinferior recess Inferior recess inferiorly the anteromedial portionsof rt and lt lung are farther separated by heart andmediastinal fat forming a inverted V-shaped areaknown as inferior recess 22. SUPRA AORTIC AREA On the left side of the mediastinum Extending from aortic arch to thoracicinlet behind the anterior mediastinum Structures are 1. left subclavian artery2. left wall of trachea3. left superior intercostal vein4. mediastinal fat Most of these structures are in middlemediastinum except left sup intercostalvein which is situated in postmediastinum 23. Retrosternal stripe, parasternal stripe, cardiac incisura On a true lateral radiograph of the chest when lung isexcluded from the retrosternal space by mediastinalfat, a vertical retrosternal opacity is often seen knownas retrosternal stripe The lung can also contact upper 2/3rd of anterior chestwall thus outlining the parasternal areas and creatingparasternal stripe..particularly prominent whenthe ant surface of lung is lobulated 24. Contd. On the left side as the sternum is followed inferiorlythe lung is normally excluded from anteromedial chestwall by cardiac apex, epicardial fat pad or both..thisdeficiency is known as cardiac incisura Sometimes subclavian arteries cause superior andposterior indentation and innominate veins causeinferior and anterior indentation.these are known asvascular incisura 25. Contd Left subclavian artery arises from aorta behind the leftcommon carotid artery and passes upward lateral tothe trachea in contact with left mediastinal pleuraforming an interface with superomedial left upper lobethus can be identified on a PA radiograph as an arcuateopacity concave laterally 26. Left subclavian artery 27. Mri demonstrate normal course of left subclavian artery 28. Aortic nipple Left sup intercostal vein has three parts aortic nipple,paraspinal portion and retroaortic part Aortic nipple consists of a rounded protruberanceadjacent to aortic arch that is created by vein seen endon as it passes anteriorly adjacent to the aortic archbefore entering the left brachicephalic vein 29. Course of left superior intercostal vein 30. Applied anatomy Seen in 1-10% patients Normally upto 4.5 mm diameter Dialatation occurs in- supine position Muller maneuvre systemic venous hypertension 31. Dilated left sup intercostal vein c/b collateral blood flow fromleft brachiocephalic vein into azygos and hemi azygos vein 32. Posterior Junction Line Seen above the level of the azygos vein and aorta and that isformed by the apposition of the lungs posterior to theesophagus. usually extend from third to fifth thoracic vertebrae. posterior junction line can be seen above the suprasternalnotch and lies almost vertical, whereas the anteriorjunction line deviates to the left 33. CT scan shows the posterior junction line (arrow), whichis formed by the interface between the lungs posteriorto the mediastinum and consists of four pleural layers 34. Posteroanterior chest radiograph shows a mass (arrow)obliterating the posterior junction line. Note that the massextends above the level of the clavicle and has a well-demarcatedoutline due to the interface with adjacent lung (arrowhead 35. Vascular pedicle On frontal chest radiography the vascular pedicleextends from thoracic inlet to top of the heart On the right side its boundary is formed by rightbrachiocephalic vein above and SVC below The left boundary is formed by left subclavian arteryabove and aortic arch below Right side of pedicle is entirely venous and left side ispurely arterial 36. Measurement of the width ofvascular pedicle On PA chest radiography from the point at which the SVCcrosses the right main bronchus to the point at which theleft subclavian artery arises from the aortic arch Normal range- 38-58 mm Correlation b/w azygos vein width and total blood volumewas poor although correlation with right atrial pressure isstronger Extravascular causes of widening of mediastinal silhouette( aortic trauma or extravasation of blood or saline infusion)resulted in widening of mediastinal vascular pedicle 37. MEASUREMENT OF VASCULAR PEDICLE 38. Infra aortic areaOn the left side extends from the aortic arch above tothe diaphragm below and from the anteriormediastinal space in front to paravertebral regionbehind Contains- left ventricle left atrial appendeges left pulmonary artery aortic arch 39. 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 40. The lateral border of aorto-pulmonarywindow isnormally concave or straight A lateral convexity shouldsuggest a mediastinalabnormality most commonlylymphadenopathy Although it may occsionallybe a normal variant caused byaccumulation of fat 41. Supra azygos area The supra-azygos area is that portion of the right sideof the mediastinum that extends cephalad from azygosarch to thoracic inlet separated from infra azygos areaby azygos vein and arch Contents-tracheal interfacesazygos and hemiazygos veins 42. Azygos and hemiazygos vein Originates as an extension of right ascending lumbarvein or right subcostal vein In the thorax it is situated in front, to the right orrarely to the left of the eighth thoracic vertebrae There it is joined by hemiazygos vein at the level of T80r T9 It finally inserts at the back of the superior vana cava 43. Tracheal interfaces Contact of the right lung in the supra azygos area withthe right lateral wall of the trachea creates a thin stripeon 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 44. Contd. Since the left subclavian artery and contiguousmediastinal fat usually relate to the left border oftrachea, a left paratracheal stripe is seldom seen Posterior tracheal stripe is a vertically oriented opacityformed by posterior wall of trachea where it comes incontact with the right upper lobe parenchyma 45. Azygos arch At the level of aortic arch the azygos vein consists ofthree parts-1. post / paraoesophageal2. middle / retrotracheal3. ant / right tracheo-bronchial angleDepending upon the distension of the vessel and depthof the supra azygos and infra-azygos recesses the veinmay be identified on a lateral x-ray as a retro trachealelongated opacity as it passes over the right mainbronchus 46. AZYGOS ARCH 47. Contd Measurement of ant portion is important in somediseases-A. portal hypertensionB. svc obstructionC. systemic venous hypertensionThe only segment that is visible on conventionalradiography is its entry point to the SVC seen as aslightly flattened elliptical opacityNormal range is 3-7 mm 48. Infra azygos area Content 1. azygo oesophageal recess2. heart 49. AZYGOESOPHAGEAL RECESS The azygos vein ascends in the posterior mediastinumin relation to the right side or front of the vertebralcolumn. The azygoesophageal recess is formed by contact ofright lower lobe with the esophagus and the ascendingportion of the azygos vein. The recess is frequently identified on well-penetratedPA radiographs as an interface that extends from thediaphragm below to the level of azygos arch above. 50. Contact b/w the right lung and the esophagus (straight arrow ) and azygos vein (curvedarrow) 51. HEART In a frontal chest radiograph the position of heart inrelation to the midline of the thorax depends largelyon the patients build. In asthenic individuals the heart shadow is almost inthe midline only projecting slightly to the left In those of stockier built it lies a little more to the leftside. 52. HEART CHAMBERS IN RELATION TO MEDIASTINUM 53. Contd In normal subjects the transverse diameter of the heartmeasured on standard PA radiographs is usually in therange of 11.5 15.5 cm. It is measured from chest radiography by calculatingcardio-thoracic ratio. A cardio-thoracic ratio of 50% is widely accepted as theupper limit of normal 54. THANK YOU