Lung Anatomy

1. Lung Anatomy Ben Barnard Department of Radiology Kimberley Hospital

2. Outline • Basic morphology • Fissures • Bronchopulmonary segments • Pulmonary vessels • Bronchial vessels • Lymphatics • Lung roots • Pleura • Radiological features

3. Basic morphology • Surfaces • Costal • Mediastinal • Apical • Diaphragmatic • Right lung • Three lobes • Left lung • Two lobes • Lingula of the upper lobe corresponds to right middle lobe

4. Lobules • One terminal bronchiole with lung tissue forms an acinus • Acinus with vessels, lymphatics and nerves form the primary lobule • Three to five primary lobules form a secondary lobule

7. Interlobar fissures • Oblique (major) fissure • Extends from T4/T5 posteriorly to the diaphragm antero-inferiorly • Left major fissure is more vertically orientated • Undulating in course • Medial aspect passes through the hilum • Lateral aspect is anterior to the medial aspect at the level of the hila and below • Above the hila, the lateral aspect is more posterior

9. Interlobar fissures • Transverse (minor) fissure • Separates upper and middle lobes of the right lung • Runs horizontally from the hilum to the anterior and lateral surfaces of the right lung • Level of the fourth costal cartilage • Posterior limit is the right oblique fissure, which it meets at the level of the 6th rib in the midaxillary line • Anatomically complete in only 33% of people and absent in 10%

10. Accessory fissures • Azygos fissure • Downward invagination of the azygos vein through the apical portion of the right upper lobe • Four pleural layers – two visceral and two parietal • Superior accessory fissure • Separates the apical segment of the right lower lobe from the other basal segments • Lies parallel and inferiorly to the transverse fissure • Passes posteriorly from the right oblique fissure to the posterior surface of the lung • Inferior accessory fissure • Separates the medial basal from the other right lower lobe segments • Also called Twining’s line • Left transverse fissure • Separates the lingula from the rest of the left upper lobe segments • Rarely seen

11. Azygos Fissure

12. Bronchopulmonary segments • Each lobe is divided into several bronchopulmonary segments • Each is supplied by • Segmental bronchus • Segmental artery • Segmental vein • Each segment is named for its supplying bronchus • Anatomy of the segmental bronchi is subject to variations – the most common being the origin of the apical segment bronchi from the trachea

15. Collateral air drift • Very little connection between segments except via • Pores of Kohn • Openings in alveolar walls • Connect adjacent alveolar lumens • Canals of Lambert • Connections between terminal bronchioles and adjacent alveoli • Allow gas and fluid transfer between segments but not between lobes • Ventilation of a segment is thus possible when its segmental bronchus is occluded = collateral air drift

16. Pulmonary arteries • Pulmonary trunk leaves pericardium and bifurcates in the concavity of the aortic arch anterior to the left main bronchus

17. Right Pulmonary Artery • Longer than the left • Passes across the midline below the carina and comes to lie anterior to the right main bronchus • It bifurcates while still in the hilum of the right lung • An artery to the right upper lobe passes anterior to the right upper lobe bronchus • Interlobar artery to the right middle and lower lobes passes with the bronchus intermedius

18. Left Pulmonary Artery • Left pulmonary artery spirals over the superior aspect of the left main bronchus to reach its posterior surface • It is attached to the concavity of the aortic arch by the ligamentumarteriosum • Pulmonary arteries further subdivide into segmental arteries that travel with the segmental bronchi, mostly on their posterolateral surfaces • Pulmonary arteries supply only the alveoli

19. Pulmonary veins • These do not follow the bronchial pattern • Tend to run in intersegmental septa • Two veins pass to each hilum from lung tissue above and below each oblique fissure • They enter the mediastinum slightly below and anterior to the pulmonary arteries • The lobar veins on the right may remain separate – such that three veins leave the right lung and enter the left atrium • The left pulmonary veins may unite and enter the left atrium as a single vessel

20. Bronchial arteries • Supply the bronchi, visceral pleura and connective tissues of the lungs • Arise from the thoracic aorta at the T5 or T6 level • Usually one right and two left bronchial arteries • Arise at the upper border of T5 • When a second bronchial artery occurs on the right, it often arises from the third intercostal artery • Bronchial arteries may also arise from the subclavian or internal mammary arteries • Tissues supplied by the bronchial arteries drain to the pulmonary or bronchial veins

22. Bronchial veins • Form two distinct systems • Deep veins • Form a network around the pulmonary interstitium • Communicate freely with pulmonary veins • Form a bronchial venous trunk that drains to the pulmonary system • Superficial veins • Drain to the azygos vein on the right and the accessory hemiazygos vein on the left

23. Lymphatics • Mediastinal lymph nodes that drain the lung are named according to position • Pulmonary nodes • Bronchopulmonary nodes • Carinal nodes • Tracheobronchial nodes • Right and left paratracheal nodes

25. Lymphatics • Lymph vessels of the lungs are in superficial and deep plexuses • Superficial plexus beneath the pleura drains around the surface of the lungs and the margins of the fissures to converge at the hila and bronchopulmonary nodes • Deep channels drain with the pulmonary vessels towards the hila • Few connections between superficial and deep plexuses except at the hila • Bronchopulmonary nodes drain to tracheobronchial nodes and paratracheal nodes and then into the bronchomediastinal trunks

26. Lung roots • Roots of the lungs are formed by structures that enter and emerge at the hila • Lie at T5-T7 level • Right lung root lies below the arch of the azygos vein and posterior to the SVC and right atrium • Left lung root lies below the arch of the aorta and anterior to the descending aorta

27. Pleura • Serous membrane that • Covers the lung (visceral pleura) • Lines the thoracic cavity (parietal pleura) • Both layers are continuous with each other anterior and posterior to the lung root • Below the hilum they hang down in a loose fold called the pulmonary ligament • This allows descent of the lung root in respiration and distension of the pulmonary veins

28. Pleura • Visceral pleura extends into the interlobar and accessory fissures • At rest the parietal pleura extends deeper into the costophrenic and costomediastinal recesses than the lungs and visceral pleura • Parietal pleura is supplied by the systemic vessels • Visceral pleura is supplied by the bronchial and pulmonary circulation

29. Imaging of the Lungs

30. CXR PA

31. CXR L Lat

32. Pulmonary angiography

33. Bronchial angiography

34. CT

35. HRCT

36. Dual-Energy CT

37. MRI

38. MRA/MRV & Dynamic Airway Imaging

39. Isotope V/Q Scanning

40. SPECT

41. PET-CT

42. What’s missing?

43. Thank you

44. References • 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 • Butler, P., Mitchell, A.W.M., Ellis, H. (1999). Applied Radiological Anatomy. Cambridge: Cambridge University Press • Karcaaltincaba M, Aktas A. Dual-energy CT revisited with multidetector CT: review of principles and clinical applications. DiagnIntervRadiol 2011; 17:181-194