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Lung Anatomy Ben Barnard Department of Radiology Kimberley Hospital Outline • • • • • • • • Basic morphology Fissures Bronchopulmonary segments Pulmonary vessels Bronchial vessels Lymphatics Lung roots Pleura • Radiological features 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 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 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 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% 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 Azygos Fissure 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 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 Pulmonary arteries • Pulmonary trunk leaves pericardium and bifurcates in the concavity of the aortic arch anterior to the left main bronchus 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 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 ligamentum arteriosum • Pulmonary arteries further subdivide into segmental arteries that travel with the segmental bronchi, mostly on their posterolateral surfaces • Pulmonary arteries supply only the alveoli 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 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 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 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 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 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 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 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 Imaging of the Lungs CXR PA CXR L Lat Pulmonary angiography Bronchial angiography CT HRCT Dual-Energy CT MRI MRA/MRV & Dynamic Airway Imaging Isotope V/Q Scanning SPECT PET-CT What’s missing? Thank you 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. Diagn Interv Radiol 2011; 17:181-194