Heart and mediastinum

Examine the cardiac outline identifying all the heart borders and the outline of the great vessels (see Figs 1.1 and 1.2). Check that there are not any abnormal densities projected through the cardiac silhouette. Look at the aortic and pulmonary artery outlines. The heart and mediastinal outline are made up of a series of 'bumps' (see Fig. 1.3). On the right side, there are right braciocephalic vessels, the ascending aorta and superior vena cava, the right atrium, and the inferior vena cava. On the left side, there are four 'moguls' in addition to the left brachiocephalic vessels: these are the aortic arch, the pulmonary trunk, the left atrial appendage and the left ventricle. The size and shape of each of these structures need to be looked at for signs of enlargement or reduction in size. The right heart border is created by the right atrium alone (the right ventricle is an anterior structure, therefore does not contribute to any heart borders) - this is a question examiners love to ask (see Fig. 1.4).

Fig. 1.1 Diagram of normal frontal chest X-ray: 1. trachea, 2. right lung apex, 3. clavicle, 4. carina, 5. right main bronchus, 6. right lower lobe pulmonary artery, 7. right artium,

8. right cardiophrenic angle,

9. gastric air bubble,

10. costophrenic angle, 11. left ventricle, 12. descending thoracic aorta, 13. left lower lobe pulmonary artery, 14. left hilum, 15. left upper lobe pulmonary vein, 16. aortic arch.

Fig. 1.1 Diagram of normal frontal chest X-ray: 1. trachea, 2. right lung apex, 3. clavicle, 4. carina, 5. right main bronchus, 6. right lower lobe pulmonary artery, 7. right artium,

8. right cardiophrenic angle,

9. gastric air bubble,

10. costophrenic angle, 11. left ventricle, 12. descending thoracic aorta, 13. left lower lobe pulmonary artery, 14. left hilum, 15. left upper lobe pulmonary vein, 16. aortic arch.

Fig. 1.2 Diagram of normal lateral chest X-ray: 1. ascending thoracic aorta, 2. sternum, 3. right ventricle, 4. left ventricle, 5. left atrium, 6. gastric air bubble, 7. right hemidiaphragm, 8. left hemidiaphragm, 9. right upper lobe bronchus, 10. left upper lobe bronchus, 11. trachea.

Fig. 1.3 The 'bumps' which make up the cardiac silhouette: 1. right brachiocephalic vein,

2. ascending aorta and superimposed SVC,

3. right atrium, 4. inferior vena cava,

5. left brachiocephalic vessels, 6. aortic arch, 7. pulmonary trunk, 8. left atrial appendage, 9. left ventricle.

Fig. 1.4 Cardiac chambers and great vessels: LA, left atrial appendage; RA, right atrium; LV, left ventricle; RV, right ventricle; IVC, inferior vena cava; SVC, superior vena cava; PA, pulmonary artery; A, ascending aorta.

Heart size can be estimated using the cardiothoracic ratio. The cardiac measurement is taken as the greatest transverse heart diameter and is compared to the greatest internal width of the thorax. A ratio of greater than 0.5 is often used in clinical practice to indicate cardiomegaly.

Look at the position of the hila and their density - compare the left with the right side. Tumours and enlarged lymph nodes can occur here making the hila appear bulky.

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