1. UNDERSTANDING HRCT THORAX

2. LUNG ANATOMY Right lung is divided by major and minor fissure into 3 lobes and 10bronchopulmonary segments Left lung is divided by major fissure into 2 lobes with a lingular lobe and 8 bronchopulmonary segments

3. ANATOMY The trachea (windpipe) divides into left and the right mainstem bronchi, at the level of the sternal angle (carina). The right main bronchus is wider, shorter, and more vertical than the left main bronchus. The right main bronchus subdivides into three lobar bronchi, while the left main bronchus divides into two. The lobar bronchi divide into tertiary bronchi, also known as segmentalinic bronchi, each of which supplies a bronchopulmonary segment.

5. ANATOMY The segmental bronchi divide into many primary bronchioles which divide into terminal bronchioles, each of which then gives rise to several respiratory bronchioles, which go on to divide into two to 11 alveolar ducts. There are five or six alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.

7. TRACHEAL ANATOMY 10-12 cm in length Extrathoracic (2-4cm) and Intrathoracic(6-9cm beyond manubrium) In men, tracheal diameter averages 19.5 mm and in women, tracheal diameter is slightly less, averaging 17.5 mm The posterior portion of the tracheal wall is a thin fibromuscular membrane termed the posterior tracheal membrane There is marked variability in the cross-sectional appearance of the trachea, which may appear convex posteriorly, flat, or convex anteriorly

8. Contains glands, small arteries, nerves, lymph vessels and elastic fibers Trachealis muscle overlies esophageal muscle and epithelium The membranous posterior membrane allows esophageal expansion during expiration

9. BRONCHIAL ANATOMY Airways divide by dichotomous branching, with approximately 23 generations of branches from the trachea to the alveoli. The wall thickness of conducting bronchi and bronchioles is approximately proportional to their diameter. Bronchi with a wall thickness of less than 300 um is not visible on CT or HRCT. As a consequence, normal bronchi less than 2 mm in diameter or closer than 2 cm from pleural surfaces equivalent to seventh to ninth order airways are generally below the resolution even of high-resolution CT

10. BRONCHUS BLOOD SUPPLY Bronchial Arteries( 2 on left side i.e. superior and inferior and 1 on right side) Left arises from thoracic aorta Right from either thoracic aorta, sup. lt. bronchial or right 3rdintercostal artery VENOUS DRAINAGE on right- azygous vein on left- left superior intercostal or accessory hemiazygous vein NERVE SUPPLY Pulmonary plexus at hilum (vagus and sympathetic)

11. BRONCHOARTERIAL RATIO (B/A) Internal diameter of both bronchus and accompanying arterial diameter calculated and ratio measured. If obliquely cut section seen, then the LEAST diameter is considered. Normal ratio is 0.65-0.70

12. BRONCHIAL WALL THICKNESS (T/D) Wall thickness proportionately decreases as the airway divides further as according to the diameter of the airway. T/D ratio approximates to 20% at any generation of airway.

13. The Nomenclature Adopted by the Ad HOC lnternational Committee Meeting at the Time of the lnternational Congress of Otorhinolaryngology in 1949 [I]"

14. The Nomenclature Adopted by the Ad HOC lnternational Committee Meeting at the Time of the lnternational Congress of Otorhinolaryngology in 1949 [I]"

17. MEDIASTINUM Broad central portion that separate the two laterally placed pleural cavities. Imaginary plane passes through T4 divides it into Superior & Inferior mediastinum Inferior mediastinum is further divided- Heart enclosed in pericardium (M) Sternum to anterior pericardium (A) Posterior pericardium to vertebrae (P)

18. INTERSTITIAL ANATOMY Lung is supported by a network of connective tissue called interstitium Interstitium not visible on normal HRCT but visible once thickened. Interstitium is constituted by AXIALfibre system (peribronchovascular & centrilobular), PERIPHERALfibre system (subpleural & interlobular septa) and SEPTALfibre system (intralobular septa)

19. Secondary Lobule It is the smallest lung unit that is surrounded by connective tissue septa. It measures about 1-2 cm and is made up of 5-15 pulmonary acini, that contain the alveoli for gas exchange. The secondary lobule is supplied by a small bronchiole (terminal bronchiole) in the center, that is parallelled by the centrilobular artery. Pulmonary veins and lymphatics run in the periphery of the lobule within the interlobular septa.

21. Every CT scan starts with a scout view, a projection image that looks like a second rate X-ray. A line on scout view tells you the level of axial cut.

22. HOUNSFIELD UNIT (HU) HU scale is a linear transformation of the original linear attenuation coefficient measurement into one in which radiodensity of distilled water at STP is defined as zero HU, while radiodensity of air at STP is defined as -1000 HU. Fat  -50 to -100 HU Blood  +30 to 45 HU Bone  >+400 HU Muscle  +40HU Contrast  +130 HU

23. APPEARANCE ON CT SCAN AIR JET BLACK FAT  MODERATELY BLACK WATER  GRAY MUSCLES  SLIGHT WHITE BONES  WHITE CALICIFICATION  DENSE WHITE

24. LUNG WINDOW

25. MEDIASTINAL WINDOW

26. BONE WINDOW

27. LOBAR AND BRONCHIAL ANATOMY ON HRCT THORAX

28. TRACHEA RIGHT APICAL SEGMENT LEFT APICAL SEGMENT

30. ESOPHAGUS RB1 LB1

33. LEFT MAIN BRONCHUS RIGHT MAIN BRONCHUS LB3 CARINA RB3 LB1,2 RB2 RB1

37. RB5 BRONCHUS INTERMEDIUS LEFT UL BRONCHUS LUL RML RIGHT ML BRONCHUS LLL RLL

41. LINGULAR BRONCHUS RB5 LB4 LB5 LB6 RLL BRONCHUS LLL BRONCHUS

43. RLL BRONCHUS LLL BRONCHUS RB6 LB6 RB7

50. RML LML MAJOR FISSURE RB8 LB8 LB9 RB10 LB10 RB9 RLL LLL

52. LB2 RB2 RB6 LB6 RB9 LB10 RB10 RB7

54. LB1,2 RB1 UL UL RB2 ML LL LL LB9

56. LB1,2 joining LUL bronchus RB1 joining RUL bronchus RC2 LC2 CARINA LB8 RB8

58. RB1 LB3 RB3 LB4 ML Bronchus RB8

60. RB3 LB3 LB5 RB5 RB4

61. VASCULAR ANATOMY ON CT THORAX

62. Rt. CCA Lt. CCA Rt. IJV Lt. IJV Rt. EJV Lt. EJV

66. Rt. CCA Rt. SCV joining Rt. BCV Lt. CCA Rt. BCV Lt. SCV Rt. SCA Lt. SCA

70. Lt. BCV joining Rt. BCV Rt. BCV Rt. BCA Lt. CCA Lt. SCA SUPRA AORTIC LEVEL

71. Formation of SVC Branching from Aortic Arch

72. AORTIC ARCH SVC AORTIC ARCH LEVEL

76. Ascending AORTA Main Pulmonary Trunk SVC Left Pulmonary Trunk Right Pulmonary Trunk Descending AORTA

79. Pulmonary Trunk arising from Right Ventricle Aorta arising from Left Ventricle SVC draining into Right Atrium Pulmonary Veins draining into Left Atrium

81. RV LV RA LA Pulmonary Veins

83. RV IVS LV DA

84. RV LV IVC DA

85. LYMPH NODE STATIONS ON CT THORAX

86. LYMPH NODES STATION IN THORAX

88. SUPRACLAVICULAR

89. STERNAL NOTCHExtends from the lower margin of the cricoid cartilage to the clavicles and the upper border of the manubrium. The midline of the trachea serves as border between 1R and 1L.

91. 2. UPPER PARATRACHEAL NODES 2R. Upper Right ParatrachealExtends to the left lateral border of the trachea. From upper border of manubrium to the intersection of caudal margin of innominate (left brachiocephalic) vein with the trachea.2L. Upper Left ParatrachealFrom the upper border of manubrium to the superior border of aortic arch.2L nodes are located to the left of the left lateral border of the trachea.

93. 3A. Pre-vascularThese nodes are not adjacent to the trachea like the nodes in station 2, but they are anterior to the vessels. 3P. Pre-vertebralThese nodes are not adjacent to the trachea like the nodes in station 2, but behind the esophagus, which is prevertebral.

95. 4. LOWER PARATRACHEAL NODES 4R. Lower Right Paratracheal From the intersection of the caudal margin of innominate (left brachiocephalic) vein with the trachea to the lower border of the azygos vein.4R nodes extend from the right to the left lateral border of the trachea. 4L. Lower Left Paratracheal From the upper margin of the aortic arch to the upper rim of the left main pulmonary artery.

97. 5-6. AORTIC NODES 5. Subaortic nodesThese nodes are located in the AP window lateral to the ligamentumarteriosum. These nodes are not located between the aorta and the pulmonary trunk but lateral to these vessels. 6. Para-aortic nodesThese are ascending aorta or phrenic nodes lying anterior and lateral to the ascending aorta and the aortic arch.

99. Inferior Mediastinal Nodes 7-9 7. Subcarinal nodes Nodes below carina 8. Paraesophageal nodes Nodes lateral to esophagus 9. Pulmonary Ligament nodes Nodes lying within the pulmonary ligaments.

101. Hilar, Lobar and (sub)segmental Nodes 10-14 These are all N1-nodes.10. Hilar nodesThese include nodes adjacent to the main stem bronchus and hilar vessels. On the right they extend from the lower rim of the azygos vein to the interlobar region. On the left from the upper rim of the pulmonary artery to the interlobar region.

103. AUDIENCE QUIZ

116. THANK YOU