The Normal Chest anatomy in radiology.pptx

Normal chest anatomy simple presentation

1. The Normal Chest

2. THE LUNGS Each lung is divided into lobes surrounded by pleura. There are normally two lobes on the left, the upper and lower, separated by the major (oblique) fissure, and three on the right, the upper, middle and lower lobes, separated by the major (oblique) and minor (horizontal) fissures. The major fissures have similar anatomy on the two sides. Each major fissure follows a gently curving plane somewhat similar to a propeller blade.

3. The minor fissure position is represented by an oval area of reduced vascularity at the level of the bronchus intermedius. In 1% of the population an accessory fissure, called the ‘azygos lobe fissure’. This fissure contains the azygos vein at its lower end.

4. THE CENTRAL AIRWAYS The trachea is a straight tube that, in children and young adults, passes inferiorly and posteriorly in the midline. In cross-section the trachea is usually round, oval or oval with a flattened posterior margin. Maximum coronal and sagittal diameters in adults on plain chest radiography are 21 and 23 mm, respectively, for women, and 25 and 27 mm for men. On CT the mean transverse diameter is 15.2 mm for women and 18.2 mm for men. Calcification of the cartilage rings of the trachea is a common normal finding after the age of 40 years, increasing in frequency with age. The trachea divides into the two mainstem bronchi at the carina. In adults the right mainstem bronchus has a steeper course than the left. The left main bronchus extends up to twice as far as the right main bronchus before giving off its upper lobe division. Lobar and segmental branching patterns :

5. THE LUNGS BEYOND THE HILA The segmental bronchi divide into smaller and smaller divisions until, after 6–20 divisions, they become bronchioles and no longer contain cartilage in their walls. Purely conducting airways are known as the terminal bronchioles, beyond which lie the alveoli. The walls of the segmental bronchi are invisible on the chest radiograph unless seen end on, when they may cause ring shadows. The acinus, which is 5 to 6 mm in diameter, comprises respiratory bronchioles, alveolar ducts and alveoli. The acini are grouped together in lobules of three to five acini, which, in the lung periphery, are separated by septa and together compose the secondary pulmonary lobule. These peripheral interlobular septa, when thickened by disease, are the so-called septal or Kerley B lines. The pulmonary blood vessels are responsible for branching linear markings within the lungs on both conventional radiographs and CT.

6. The lower lobe veins run more horizontally and the lower lobe arteries more vertically. The upper lobe arteries and veins show a similar gently curving vertical orientation. The diameter of the artery is usually much the same as the diameter of the bronchus (4 to 5 mm). Diameter of over 1.5 times the diameter of the adjacent bronchus indicates that the vessel is increased in size. Vessels in the first anterior interspace should not exceed 3 mm in diameter. A rich network of lymphatic vessels drains the lung and pleura to the hilar lymph nodes. In normal circumstances the lymphatic network is invisible radiographically but when thickened the septa are seen as line shadows known as septal or Kerley lines. Thickened interlobular septa correspond to Kerley B lines and thickened deep septa correspond to Kerley A lines.

7. THE HILA The major points to remember when viewing the hila are the following: 1)The transverse diameter of the lower lobe arteries before their segmental divisions measure 9 to 16 mm on the normal posteroanterior (PA) chest radiograph. 2) The posterior walls of the right main bronchus and its division into the right upper lobe bronchus and bronchus intermedius are outlined by air and appear as a thin stripe on lateral plain radiographs and on CT. On the left are rarely visible on the plain radiograph because the left lower lobe artery intervenes between the lung and the bronchial tree. 3) The right pulmonary artery passes anterior to the major bronchi, whereas the left pulmonary artery arches superior to the left main bronchus. 4) On lateral chest radiographs the angles between the middle and right lower lobe bronchi on the right, and the upper and lower lobe bronchi on the left, do not contain any large end-on vessels; a rounded shadow of greater than 1 cm in these angles is, therefore, unlikely to be a normal vessel. 5) The pulmonary veins are usually similar on the two sides .

8. THE MEDIASTINUM The mediastinum is divided into superior, anterior, middle and posterior compartments. The blood vessels, trachea and main bronchi make up the bulk of the mediastinum. The thymus is situated anterior to the aorta and right ventricular outflow tract or pulmonary artery; it is often best appreciated on a section through the aortic arch or great vessels. In adults the thymus is bilobed or triangular in shape. The maximum width and thickness of each lobe decreases with advancing age. In younger patients, the CT density of the thymus is homogeneous and close to that of other soft tissues, but after puberty the density gradually decreases owing to fatty replacement. Residual thymic parenchyma, which may be visible as streaky or nodular densities within the fat. Lymph nodes are widely distributed in the mediastinum. Ninety-five per cent of normal mediastinal lymph nodes are less than 10 mm in diameter, and the remainder, with few exceptions, are less than 15 mm in diameter.

9. Tumour –nodes–metastasis (TNM) classification for lung cancer proposed by the International Association for the Study of Lung Cancer (IASLC): This classification groups nodal stations into seven anatomical zones: supraclavicular, upper, aortopulmonary, subcarinal, lower, hilar and peripheral.

10. Junction Lines: When there is only a small amount of fat anterior to the ascending aorta and its major branches, the two lungs may be separated anteriorly by little more than the four intervening layers of pleura. In such patients an anterior junction line is visible on frontal chest radiographs. The lungs may also come close together behind the oesophagus , forming the posterior junction line . The major value of being able to identify the anterior and posterior junction lines is that a mass, or other space-occupying process, in the junctional areas can be excluded if these lines are visible.

11. Right Mediastinum Above the Azygos Vein: The right superior mediastinal border is formed by the right brachiocephalic vein and the superior vena cava. With aortic or brachiocephalic artery ectasia or unfolding, either of these veins may be pushed laterally or the mediastinal border may be formed by the aorta or the right brachiocephalic artery. Lung contacts the right tracheal wall from the level of the clavicles down to the azygos vein, producing a visible stripe of uniform thickness known as the right paratracheal stripe. Value of this stripe is that its presence excludes a space-occupying process in the area where the stripe is visible. The lung posterior to the trachea contacts the right wall of the oesophagus . If the oesophagus at this level contains air, then the right wall of the oesophagus is seen as a stripe, the so-called oesophageal – pleural stripe.

12. Left Mediastinum Above the Aortic Arch : The mediastinal shadow to the left of the trachea above the aortic arch is of low density and is caused by the left carotid and left subclavian arteries together with the left brachiocephalic (innominate) and jugular veins. Trachea and Retrotracheal Area in the Lateral View : The course of the trachea on a normal lateral view is straight, or bowed anteriorly in patients with aortic unfolding. Its anterior wall is visible in a minority of patients, but the posterior wall is usually seen because lung often passes behind the trachea, thereby permitting visualisation of the posterior tracheal (stripe) band. If a large amount of air is present in the oesophagus , the posterior tracheal band may be much thicker, as it then comprises the combined thicknesses of the posterior tracheal wall and the anterior oesophageal wall.

13. Supra-Aortic Mediastinum on the Lateral View : A variable proportion of the aortic arch and its major branches is visible on the lateral view, depending largely on the degree of aortic unfolding. The left brachiocephalic vein is seen as an extrapleural bulge behind the manubrium in a small proportion of normal people .

14. Right Middle Mediastinal Border Below the Azygos Arch : Below the azygos arch, the right lower lobe makes contact with the right wall of the oesophagus and the azygos vein as it ascends next to the oesophagus . This portion of the lung is known as the azygo-oesophageal recess, and the interface is known as the azygo-oesophageal line. Convex shape suggests the presence of a subcarinal mass or left atrial enlargement

15. Paraspinal Lines : Lymph nodes and intercostal veins occupy the space between the spine and the lung. In individuals with little fat, the interfaces, known as the paraspinal lines. Retrosternal Line : The band-like opacity simulating pleural or extrapleural disease is often seen along the lower third of the anterior chest wall on a lateral chest radiograph . The left lung does not contact the most anterior portion of the left thoracic cavity at these levels because the heart occupies the space. The band-like opacity is, therefore, accounted for by the normal heart and mediastinum, rather than by disease.

16. THE DIAPHRAGM The diaphragm consists of a large dome-shaped central tendon surrounded by a sheet of striated muscle which is attached to ribs 7 to 12 and to the xiphisternum. The normal right hemidiaphragm is found at about the level of the anterior portion of the sixth rib, with a range of approximately one interspace above or below this level. The right hemidiaphragm is 1.5 to 2.5 cm higher than the left. The mean excursion of the right hemidiaphragm on deep inspiration being 53 mm and that of the left being 46 mm. Incomplete muscularisation , known as eventration. An eventration is composed of a thin membranous sheet replacing what should be muscle.

17. A linear density arising from the lateral wall of the inferior vena cava is often seen coursing over the surface of the right hemidiaphragm. This line represents pleura and an envelope of fat investing the phrenic nerve.

18. THANK YOU