Chest Radiography




Chest radiography was an essential part of cardiac evaluation before echocardiography and Doppler studies became widely available to cardiologists. This simple test remains very useful to physicians who do not have access to echocardiography and Doppler studies. Cardiovascular abnormalities may be incidentally suspected by x-ray films that were obtained for other reasons. Chest Radiography also supplements information that is not gained by the echocardiography study, such as information on the lung parenchyma, airways, and vascular structures connected to the heart.


Chest radiographic films can provide the following information: heart size and silhouette; enlargement of specific cardiac chambers; pulmonary blood flow or pulmonary vascular markings; and other information regarding lung parenchyma, spine, bony thorax, abdominal situs, and so on. Posteroanterior and lateral views are routinely obtained.


Heart Size and Silhouette


Heart Size


Measurement of the cardiothoracic (CT) ratio is by far the simplest way to estimate the heart size in older children ( Fig. 4-1 ). The CT ratio is obtained by relating the largest transverse diameter of the heart to the widest internal diameter of the chest:


<SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='CT ratio=(A+B)−C’>CT ratio=(A+B)−CCT ratio=(A+B)−C
CT ratio = ( A + B ) − C
where A and B are maximal cardiac dimensions to the right and left of the midline, respectively, and C is the widest internal diameter of the chest. A CT ratio of more than 0.5 indicates cardiomegaly. However, the CT ratio cannot be used with accuracy in newborns and small infants, in whom a good inspiratory chest film is rarely obtained. In this situation, the degree of inadequate inspiration should be taken into consideration. Also, an estimation of the cardiac volume should be made by inspecting the posteroanterior and lateral views instead of the CT ratio.


FIGURE 4-1


Diagram showing how to measure the cardiothoracic (CT) ratio from the posteroanterior view of a chest radiographic film. The CT ratio is obtained by dividing the largest horizontal diameter of the heart (A + B) by the longest internal diameter of the chest (C).


To determine the presence or absence of cardiomegaly, the lateral view of the heart should also be inspected. For example, isolated right ventricular enlargement may not be obvious on a posteroanterior film but will be obvious on a lateral film. In a patient with a flat chest (or narrow anteroposterior diameter of the chest), a posteroanterior film may erroneously show cardiomegaly.


An enlarged heart on chest radiographs more reliably reflects a volume overload than a pressure overload. Electrocardiograms (ECGs) better represent a pressure overload than chest radiographic films.


Normal Cardiac Silhouette


The structures that form the cardiac borders in the posteroanterior projection of a chest roentgenogram are shown in Figure 4-2 . The right cardiac silhouette is formed superiorly by the superior vena cava (SVC) and inferiorly by the right atrium (RA). The left cardiac border is formed from the top to the bottom by the aortic knob, the main pulmonary artery (PA), and the left ventricle (LV). The left atrial appendage (LAA) is located between the main PA and the LV and is not prominent in a normal heart. The right ventricle (RV) does not form the cardiac border in the posteroanterior view. The lateral projection of the cardiac silhouette is formed anteriorly by the RV and posteriorly by the left atrium (LA) above and the LV below. In a normal heart, the lower posterior cardiac border (i.e., LV) crosses the inferior vena cava (IVC) line above the diaphragm (see Fig. 4-2 ).




FIGURE 4-2


Posteroanterior and lateral projections of normal cardiac silhouette. Note that in the lateral projection, the right ventricle (RV) is contiguous with the lower third of the sternum and that the left ventricle (LV) normally crosses the posterior margin of the inferior vena cava (IVC) above the diaphragm. AO, aorta; LA, left atrium; LAA, left atrial appendage; LPA, left pulmonary artery; PA, pulmonary artery; RA, right atrium; RPA, right pulmonary artery; SVC, superior vena cava.

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Apr 15, 2019 | Posted by in CARDIOLOGY | Comments Off on Chest Radiography

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