4 chest x-ray - springerextras.springer.com/2007/978-1-84628-188-4/fscommand/pdfs/004.pdf · chest...

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Chest X-RayMary Ella Round

Key Points

• Chest x-ray is perhaps the simplest radiologic test, and yet it is highly valuable, as it can be used to diagnose and assess the severity of cardiovascular diseases and the response to therapy.

• Optimal image acquisition is essential for the proper interpretation of the fi ndings on a chest x-ray.

• To reduce oversights, a consistent approach to fi lm inter-pretation should be followed for each observation.

• A “good” inspiratory effort is indicated by the right hemi-diaphragm being inferior to the eighth posterior right rib. If an image is obtained during expiration, the cardiac silhouette appears larger and the pulmonary markings are more prominent.

• The interpretation of the cardiac size, silhouette, and pulmonary parenchymal markings depends on the posi-tioning and projection of the patient.

• An increased or “splayed” angle of carina suggests eleva-tion of the left mainstem bronchus secondary to left atrial enlargement as seen in cardiomyopathy or mitral stenosis.

• Visualizing the edge of the lung is necessary for diagnos-ing a pneumothorax.

• Pulmonary vascular markings are normally distinct. Indistinct markings, fi ssural thickening, and septal lines suggest vascular congestion and radiographic diagnosis of congestive heart failure.

• The cardiac diameter divided by the widest chest diame-ter should be less than 60%. The average value is 45% in a 70-kg man.

• The volume of the left ventricle must increase by approx-imately 66% in order to produce an abnormal cardiotho-racic ratio.

• A dilated right ventricle will not affect the cardiothoracic ratio.

• In the lateral view on a chest x-ray, a line drawn from the junction of the sternum and diaphragm to the carina will

pass through the aortic valve, while the mitral valve and its annulus lie posterior and inferior to that diagonal.

• Aortic dissection is not a plain chest fi lm diagnosis.• Pulmonary venous pressure greater than 10 to 12 mm Hg

results in redistribution or “cephalization” of blood from the lung bases into the upper lobe vessels, while peribron-chial “cuffi ng” and fl uid accumulation in the interlobu-lar septa, referred to as Kerley B lines, suggest a pulmonary venous pressure between 20 and 30 mm Hg. Elevated pulmonary venous pressure greater than 30 mm Hg demonstrates symmetric small parenchymal densities in addition to the above fi ndings.

• Pulmonary arterial hypertension is manifested by decreased caliber of the lower lobe segmental arteries (pruning) and dilatation of the central or main pulmo-nary arteries.

• Radiographic signs do not correlate well with pulmonary embolic disease, and further testing is required, if clini-cally suspicious.

• Fewer than 10% of the patients with pulmonary embo-lism show the classic signs referred to as the Hampton’s hump, the Westermark sign, and the Fleischner sign.

• Radiographic fi ndings on a chest x-ray are similar in car-diomegaly and pericardial effusion.

Conventional chest radiography remains one of the most frequently ordered radiologic examinations in clinical cardi-ology. Chest radiographs are universally available, relatively inexpensive, and cost-effective. The exam can be used to assess patient response to therapy or to monitor the status of cardiovascular disease.

This chapter is limited in its scope. A brief summary of radiographic technique is provided. Radiographic fi ndings in the normal patient population and the critically ill are addressed. A sample algorithm for evaluating the chest radio-graph is presented. Finally, radiographic interpretation specifi cally as it pertains to cardiovascular disease is reviewed.

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Principles of Chest Radiography. . . . . . . . . . . . . . . . . . . . . 80Pathophysiologic Principles Pertaining to the

Radiographic Signs of Cardiovascular Disease . . . . . . 86

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

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Principles of Chest Radiography

Principles of Radiologic Technique

An x-ray is a bundle of electromagnetic energy called a photon. The average energy of an x-ray photon is 30 kiloelec-tron volts (keV). Radiographic image production entails the x-ray photons passing through tissue and interacting with an image receptor. The image receptor can be a radiographic fi lm. In computed radiology or digital imaging, the image receptor is a computer chip that can store and display the radiographic image on a digital screen. The quantity and quality of the x-ray beam affects the interaction within various tissues in the body. Conversely, the composition of the anatomic tissues affects the x-ray beam interaction. The radiation that exits the patient will have varying energies, which can translate to different shades of gray on the image receptor.1

To create an image the x-rays must be absorbed at differ-ent levels. The interaction of the x-ray with matter may be one of three interactions—the x-ray may be absorbed, scat-tered, or transmitted. X-rays can pass through the lung paren-chyma unimpeded, but they cannot pass through the vertebral body. The image receptor then detects the differen-

tial absorption and the image documents a contrast between the lung parenchyma and the vertebral body.

The purpose of the conventional chest radiograph is to visualize clearly the thoracic anatomy on the posterior ante-rior (PA) and lateral radiographs. Optimal chest x-ray images are the product of appropriate utilization of peak kilovoltage, amperage, and time expressed as milliampere-seconds2 (Fig. 4.1). The kilovoltage peak (kVp) determines the maximum energy of the emitted photons from the x-ray tube. The mil-liampere-seconds (mAs) measures the tube current and expo-sure time in seconds. This parameter determines the number of photons emitted. Typically chest radiographs are per-formed at 120 kVp and 5 mAs. Equally important factors include characteristics of the x-ray generator, the target fi lm distance (72 inches), compatible fi lm–screen combinations, and the appropriate use of a grid. Depending on the clinical question, these factors can be altered to best visualize the anatomy in question. For example, the technical exposure factors can be altered to visualize the ribs or lungs. Overex-posure of the chest x-ray is appropriate in patients sustaining blunt trauma in which it is critical to visualize the medias-tinal soft tissue structures and the pulmonary parenchyma behind the heart (Fig. 4.2). A higher mA, however, also could lead to secondary or scattered Compton radiation, which is

FIGURE 4.1. The cardiac silhouette, pulmonary vasculature, pul-monary parenchyma, diaphragmatic surfaces, and costophrenic angles should all be clearly visible without the use of a “bright” light in both the posteroanterior (PA) (A) and the lateral (B) projections.

The technical factors used to obtain this PA radiograph (A) were 110 kVp and 1.6 mAs and, for the lateral (B), 110 kVp and 6.5 mAs.


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often referred to as “fog” as it can obscure the pulmonary interstitium, bronchi, and pulmonary vessels (Fig. 4.3).

Conventional fi lm–screen radiography is limited by these technical parameters. Once a conventional image is pro-

cessed, the image is permanent and further adjustments cannot be made. This can sometimes result in repeating the image to answer clinical questions. Digital imaging can record a wider range of tissues with one exposure. This

FIGURE 4.3. Effect of secondary (Compton) radiation “fog” on “image clarity” in the same patient as in Figure 4.1: 110 kVp and 1.6 mAs (A); 110 kVp and 6.9 mAs (B). (A) The image is “sharp” and

the pulmonary parenchyma and vasculature are clearly demon-strated. (B) Radiation “fog” diminishes image clarity, particularly as it relates to the lungs and the pulmonary vasculature.

FIGURE 4.2. “Overpenetrated” PA (A) and lateral (B) chest x-rays of the patient as in Figure 4.1 obtained with 120 kVp and 3.0 mAs. This technique demonstrates the thoracic spine through the heart

at the expense of “burning out” the lungs, including the pulmonary vasculature.


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information provides quantitative data on the attenuation characteristics of the tissues to visualize the thorax with or without overlying structures. Radiographic images can now be obtained, interpreted, processed, stored and retrieved more quickly.3 Computed radiography (CR) or digital radiog-raphy has largely replaced conventional screen–fi lm combi-nation techniques. A common technique in CR uses a photostimulable phosphor plate within a cassette to store transmitted x-rays. An exposed cassette is scanned with a low-energy laser beam to encode the digital image. Newer technologies include using a photoconductor such as amor-phous selenium to convert x-rays directly into electrical charges. This technique is used in digital radiography (DR).3

Principles Regarding the Chest X-Ray

The routine chest radiograph includes the posteroanterior (PA) and lateral projections. Each is obtained with the patient erect and in deep inspiration if the patient is able. Ideally, patients are imaged without overlying radiopaque foreign bodies or artifacts. Chest radiographs are obtained usually with a high kilovoltage and milliamperage to decrease expo-sure time and cardiac motion.

Posteroanterior (PA) refers to the direction of the x-ray beam through the chest. The patient is positioned with the anterior chest wall closest to the fi lm. The lateral chest x-ray is obtained with the patient’s left side closest to the fi lm. This positioning coupled with the x-ray source 72 inches from the detector results in the most radiographically accu-rate representation of the cardiac size.

Patients who are unable to be imaged in the radiology department may require portable chest radiography exami-nations. The cassette is placed behind the patient and the

projection is anterior to posterior or anteroposterior (AP). Obtaining radiographs at maximum inspiration is limited in this setting. Since the patient is supine or semierect, the blood fl ow is redistributed to the upper lobe pulmonary veins and the heart is magnifi ed.4

Inspiratory effort is evaluated by the diaphragmatic excursion. A “good” inspiratory effort is indicated by the right hemidiaphragm being inferior to the eighth posterior right rib (Fig. 4.4). When evaluating patients with more com-pliant lungs, the 11th rib may be visualized. Frequently patients with chronic obstructive pulmonary disease will also demonstrate an increased inspiratory lung volume. The right hemidiaphragm is usually higher than the left. If an image is obtained during expiration, the cardiac silhouette appears larger and the pulmonary markings are more prominent.

Normal Chest X-Ray

The normal anatomic landmarks of the mediastinum visual-ized on the PA radiograph include the aorta, the lateral margin of the left subclavian artery, the aorticopulmonary clear space or “window,” the main pulmonary artery, the lateral margin of the left auricular appendage, the lateral margin of the left ventricle, and, on the right, the brachioce-phalic artery, the superior vena cava, and the lateral margin of the right atrium (Figs. 4.5 to 4.7).

The right hilum is typically higher than the left. The hilar densities are composed mainly of right and left main pulmonary arteries and their primary divisions. The azygous vein is seen at the junction of the trachea and the right main-stem bronchus.

The carina and the bronchi are best visualized on the PA radiograph. Usually the carina angle is acute. If the angle is

FIGURE 4.4. Effect of inspiration (A) and expiration (B) of the same patient as in Figure 4.1 obtained within minutes of each other. (B) In expiration, both the superior mediastinum and the cardiac silhouette increased in transverse diameter.


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FIGURE 4.5. Normal PA chest x-ray shows, along the left side of the cardiac silhouette, from superior to inferior, the lateral margin of the left subclavian artery (straight black arrow), the aortic arch (asterisk) the aorticopulmonary window (arrowhead), the main pul-monary artery (p), the left auricular appendage (open black arrow), and the lateral wall of the left ventricle (large white arrow). On the right, the superior vena cava (curved black arrow), the azygos vein (small white arrow), and the wall of the right atrium (curved open arrow) are visible.

FIGURE 4.6. Normal chest x-ray. (A) PA. (B) Lateral. Major land-marks on cardiac silhouette are marked. RA, right atrium; LV, left ventricle.

increased or “splayed,” then the elevation of the left main-stem bronchus may be secondary to left atrial enlargement as seen in cardiomyopathy or mitral stenosis.

On the lateral chest x-ray, normal anatomic landmarks include the anterior wall of the right atrium, the posterior segment of the aortic arch and the proximal descending aorta, the posterior left atrium, the posterior left ventricle, and the inferior vena cava. The retrosternal clear space is a radiolucent area posterior to the sternum and anterior to the ascending aorta. Right ventricular enlargement may encroach upon the retrosternal clear space. Left ventricular enlarge-ment is noted on the lateral exam when the left ventricle border projects greater than 2 cm behind the inferior vena cava (Fig. 4.7B).

The lobar pulmonary arteries arise from the main pul-monary arteries.5–7 The lobar arteries accompany the lobar and segmental bronchi branching out from each hilum. In the upper lobes, the pulmonary arteries extend superolater-ally from the superior portion of the hilum. The arterial margins are normally sharply defi ned. The arteries branch and gradually diminish in caliber. The upper lobe veins are less numerous than the pulmonary arteries. Normally, the


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pulmonary arteries, bronchi, veins, and accompanying inter-stitial tissue are visible up to 2 cm from the visceral pleural surface over the convexity of the lung (Fig. 4.8).

The lower lobe arteries and veins extend inferiorly and laterally from the inferior aspect of the hila.6 There is a dif-ference in the size of the pulmonary vessels in the upper lung zones compared with the lower, as a result of pressure varia-tion in the blood fl ow from the apex to base. A similar volume of lung at the base of the lung has a four to eight times increased blood fl ow as a similar volume at the apex.8 These fi ndings are not so apparent on the supine radiograph.

Principles for Assessing the Radiographic Examination

A consistent approach to fi lm interpretation should be fol-lowed for each observation. Some clinicians interpret images from the center radiating outward or vice versa. The approach is not as important as a consistent algorithm. This provides the observer with a system to evaluate areas of secondary interest that might otherwise be forgotten. This suggested approach or checklist may help in evaluating car-diovascular disorders while starting with areas of secondary interest.

FIGURE 4.7. Relationship of the posterior wall of the left ventricle to the inferior vena cava on a lateral chest x-ray as an estimate of cardiac size. (A) On the erect PA chest x-ray, the heart appears enlarged with left ventricular preponderance. (B) However, on the lateral chest x-ray, the distance between the inferior vena cava (arrowheads) and the posterior wall of the left ventricle (arrows) is less than 2 cm (double-ended arrow), indicating that the heart is not enlarged.



Assessing the chest radiograph should begin with assess-ing the patient identifi cation parameters and date, including the year. Appropriate comparison x-rays or complementary studies should be available for possible correlation. Briefl y the positioning of the patient and the projection of the radio-graph should be noted. Posterior and lateral imaging is not always possible in the acutely ill patient. The interpretation of the cardiac size, silhouette, and pulmonary parenchymal markings depends on the positioning and projection of the patient (Fig. 4.9). In the critically ill patient evaluation may start with overlying or indwelling lines and tubes.9 A list of possible lines and tubes that one may fi nd in a critically ill patient is shown in Table 4.1.

Considering chest x-ray fi ndings outside the thorax fi rst may be helpful to identify secondary fi ndings. The soft tissues may give clues of trauma or prior surgeries. Cardiac surgery, thyroid procedures, and breast surgeries are frequently noted by surgical clips or wires. Next, evaluation of the abdomen can exclude intraperitoneal gas or spleno-megaly. Visualizing the bowel gas pattern is also important. Evaluating the bony thorax for subtle cough fractures may also explain chest pain in the cardiology patient. Back pain

FIGURE 4.8. Normal left upper lobe pulmonary vasculature as seen on an erect PA chest x-ray. The pulmonary arteries (a) extend upward from the superior aspect of the hilum in an arborizing pattern as they leave the hilum, the arteries are 3 to 4 mm in width with sharply defi ned margins. The arteries branch, taper, and gradu-ally disappear as they approach the periphery of the lung. A left upper lobe vein (v) is visible in the second anterior interspace lateral to the arteries. It extends obliquely downward toward the left atrium in a course that is inconsistent with its arising from the pulmonary artery.

FIGURE 4.9. Effect of erect (A) and supine (B) posture on the PA chest x-ray of the same patient obtained within minutes of each other. (A) The erect PA chest x-ray was obtained with a target fi lm distance (TFD) of 72 inches and in deep inspiration. (B) The supine chest x-ray was obtained at a TFD of 46 inches and in deep inspira-tion. Recumbency produces positional redistribution of blood throughout the cardiovascular system, resulting in increased trans-verse diameter of the superior mediastinum and the cardiac silhou-ette as well as increased width of the upper lobe vessels.


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from a thoracic aortic aneurysm may be suggested clinically; however, careful evaluation of the thoracic vertebral bodies may document a compression wedge fracture. The pleura should be evaluated for a pneumothorax or pleural effusion. Visualizing the edge of the lung is necessary for diagnosing a pneumothorax. In the supine patient the air migrates anteromedially and can outline the heart. The upright exam may show a pneumothorax at the apex of the lung. A pleural effusion can be diagnosed as a crescent or meniscus in the lateral or posterior costophrenic sulcus. Evaluating the lungs for an infectious or neoplastic abnormality may be the most natural evaluation of the chest x-ray. Evaluating the lungs in the middle of the algorithm ensures that secondary fi ndings will not be missed. The pulmonary vascular markings should be evaluated for three separate fi ndings. Pulmonary vascular markings are normally distinct. If the markings appear indistinct, vascular congestion should be considered. Fis-sural thickening and septal lines are two other radiographic signs to include in the imaging diagnosis of congestive heart failure. Classically, the redistribution of pulmonary blood fl ow is used to make the diagnosis of heart failure. Patients in congestive heart failure may not be able to stand or gener-ate a deep inspiratory effort to demonstrate these fi ndings on the supine or semierect anterior posterior portable chest radiograph.

Finally, the evaluation of the cardiac and mediastinal silhouettes can proceed. Checking the width of the medias-tinum and the contour can help the diagnosis of tumors, aneurysms, or lymphadenopathy. Many factors contribute to the mediastinal contour including patient positioning as well as the projection of the radiograph (Fig. 4.9). With aging, the mediastinum may widen from vascular tortuosity. Even the depth of inspiration affects the contour (Fig. 4.4). Subtle abnormalities may be missed on chest radiographs and further evaluation with other cross-sectional modalities such as computed tomography (CT) may be necessary.

The size and shape of the heart are determined by both the pericardium and the heart. A pericardial effusion and

cardiomegaly can look the same on a chest x-ray. It is impor-tant to evaluate the cardiothoracic ratio. A false-positive diagnosis of cardiomegaly is possible in the supine AP exam at poor inspiratory effort. When there is a question of cardiac size or a pericardial effusion, echocardiography would best evaluate the heart. A useful list for assessing a chest x-ray is shown in Table 4.2.

Pathophysiologic Principles Pertaining to the Radiographic Signs of Cardiovascular Disease

Heart

The cardiac silhouette should be evaluated for size and con-fi guration, signs of chamber preponderance (the chest x-ray does not distinguish between chamber dilatation and hyper-trophy), cardiovascular disease, coronary calcifi cation, and left ventricular aneurysm.

A normal cardiac silhouette size may be determined by the cardiothoracic ratio. The PA view should be used. The cardiac diameter divided by the widest chest diameter should be less than 60%.10 The average value is 45% in a 70-kg man.10 The volume of the left ventricle must increase approx-imately 66% in order to produce an abnormal cardiothoracic ratio.11 Since the right ventricle does not contribute to the cardiac silhouette, a dilated right ventricle will not affect the cardiothoracic ratio. An accurate chest x-ray assessment of cardiac size is obtained from the inferior vena cava to the left ventricular wall distance.

TABLE 4.1. Lines, tubes, and devices in a critically ill patient

Percutaneous indwelling central catheterCentral venous catheterPulmonary artery catheterIntraaortic balloon pumpPacemakerCardiac defi brillatorLeft ventricular assist deviceEndotracheal tubeTracheostomy tubeIntratracheal oxygen catheterStentsFeeding tubeNasogastric tubeIntraesophageal monitorTemperature probepH probeChest tube

TABLE 4.2. Chest x-ray evaluation

Check identifying parameters and date of examRecognize the positioning of the patient, inspiratory effort, and projectionLines, tubes, and cardiac devicesSoft tissues Thyroid, breast, and cardiac proceduresUpper abdomen Bowel gas pattern, free intraperitoneal air, splenomegalyBones Cough fractures, surgeries, compression fractures, metastasisPleura Pleural effusion, pneumothoraxLungs Neoplasm, infl ammatory processPulmonary vascular markings Indistinctness, septal lines, fi ssural thickeningMediastinum (may best be evaluated by CT) Tumor, lymphadenopathy, aortic pathologyCardiac pericardial silhouettes (may best be evaluated by echocardiography)Cardiomegaly, pericardial effusionPathophysiologic principles pertaining to the radiographic signs of cardiovascular disease



Valves

Cardiac valves are not visualized on a chest x-ray unless they are calcifi ed, typically at the annulus. Annular calcifi cation usually involves the aortic and mitral valves and is relatively common in the elderly. Aortic valve calcifi cation, on a chest x-ray, is best located by following the ascending aorta down-ward to its origin at the valve in the PA view. In the lateral view on a chest x-ray, a line drawn from the junction of the sternum and diaphragm to the carina will pass through the aortic valve, while the mitral valve and its annulus lie pos-terior and inferior to that diagonal (Fig. 4.10).

Calcifi cation of the mitral annulus is typically broad, irregular and most commonly appears in a reversed C or J confi guration to the left of the spine and caudal to the atrial appendage on the PA view of a chest x-ray.

Aorta

The diagnosis of acute aortic dissection must be considered in any patient with the appropriate clinical symptoms and aortic ectasia or laminar aortic calcifi cation.12–14 However, aortic dissection is not a plain chest fi lm diagnosis. The diagnosis can be established or excluded with an intravenous contrast–enhanced helical CT. Other methods used to make

the diagnosis of aortic dissection include aortography, trans-esophageal echocardiography, and magnetic resonance imaging (MRI).

Aortic aneurysms can present as a mass immediately adjacent to or indistinguishable from the aortic contour. Leaking aneurysms may widen the mediastinum and are associated with a hemothorax.

Pulmonary Vasculature

Pulmonary vasculature alterations do refl ect altered pulmo-nary hemodynamics.15–17

Pulmonary Venous Hypertension

Elevated pulmonary venous pressure is associated with car-diomegaly. Occasionally pleural fl uid collections develop. Pulmonary venous pressure greater than 10 to 12 mm Hg results in redistribution or “cephalization” of blood from the lung bases into the upper lobe vessels. Redistribution is man-ifested on the erect PA chest x-ray by an increase in the number and caliber of upper lobe vessels. The upper lobe vessels extend further toward the pleura. The upper lobe vessels remain sharply demarcated (Fig. 4.11).

FIGURE 4.10. Cardiac valve sites. (A) On the lateral chest x-ray, the aortic valve (arrow) lies on or above a diagonal line connecting the junction of the sternum and the diaphragm with the carina. (B) On the frontal chest x-ray, the location of the mitral valve is indicated

by its prosthesis (arrow), and the location of the tricuspid is shown by the upward arc (arrowhead) in the cable of the right ventricular electrode.


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FIGURE 4.12. Interstitial pulmonary edema. (A) The normal radio-graphic appearance of this patient’s right lung. Note, particularly, the medial right upper lobe artery (arrows) and the wall of the bron-chus (arrowhead). (B) Signs of interstitial edema include an increase

in the number and caliber of right upper lobe vessels whose margins are now indistinct (arrows, compare with A) and peribronchial “cuffi ng” (arrowheads), all representative of elevated pulmonary venous pressure with interstitial pulmonary edema.

FIGURE 4.11. Elevated pulmonary venous pressure without pulmo-nary edema. This 18-year-old patient has a ventricular septal defect, as refl ected by the cardiac confi guration. The intrinsic pulmonary hypervolemia results in increased caliber of the upper lobe vessels, whose margins remain distinct. There is no peribronchial cuffi ng.

Pulmonary venous pressure between 20 to 30 mm Hg results in peribronchial “cuffi ng” (Fig. 4.12). The pulmonary vessels are indistinct. Fluid accumulation in the interlobular septa is evidenced by Kerley B lines. These are 1.0-cm, linear, pleura-based densities visible on the lateral chest wall on the PA chest x-ray and retrosternally on the lateral radiograph.

Elevated pulmonary venous pressure greater than 30 mm Hg demonstrates symmetric small parenchymal den-sities in addition to the fi ndings described at lesser pressures. Kerley A lines are 2 to 3 cm long irregular linear densities 1 mm in width. These course obliquely from the lung to the hilum and represent lymphatic channels (Fig. 4.13). These fi ndings may be manifest in other conditions. For example, thickening of the interlobular septa or fi ssures may be seen in anthracosis, hemosiderosis, occupational exposure, viral pneumonia, or lymphangitic spread of carcinoma.



Abrupt or severe cardiac decompensation secondary to a massive myocardial infarction or ruptured valvular leafl ets may result in a central symmetric consolidation.7

Pulmonary Arterial Hypertension

On the PA chest x-ray pulmonary arterial hypertension is manifested by decreased caliber of the lower lobe segmental arteries and dilatation of the central or main pulmonary arteries (Fig. 4.14). In chronic obstructive pulmonary disease, precapillary hypertension results in spasm of precapillary arterioles. Persistent arterial hypertension causes the spasm to move progressively proximally to involve the small arter-ies. Persistent spasm results in hypertrophy and hyperplasia of the muscular layer or media of the arteries that further elevates pulmonary artery pressure. Classically, the radio-graphic appearance of pulmonary artery hypertension is referred to as “pruning” of the pulmonary arteries. The pathophysiology demonstrates the distal vessels to appear normal with hypertrophy of the central pulmonary arteries and early divisions.

Pulmonary Embolism

The chest x-ray is usually the fi rst imaging study performed when pulmonary embolic disease is suspected and it is usually nonspecifi c. One large study concluded the chest radiograph to be normal in 12% of patients with pulmonary emboli.18,19 Radiographic signs do not correlate well with pulmonary embolic disease, and further testing is required if clinically suspicious.18 Nonetheless, it is important to use chest radiographs to exclude other causes of disease, such as

FIGURE 4.13. Alveolar pulmonary edema. (A) On the PA chest x-ray, pulmonary vasculature is almost completely obscured by the bilateral symmetric alveolar pattern parenchymal densities. Peri-bronchial “cuffi ng” (arrowhead) is marked. (B) The lateral chest x-ray shows the “rosette” character of the alveolar fl uid, unsharpness of the interlobar fi ssures (arrows) representative of subpleural edema, and a small pleural effusion (arrowhead).

FIGURE 4.14. Pulmonary arterial hypertension, seen in a PA chest x-ray of this patient with chronic obstructive pulmonary disease, is manifest by dilation of the main pulmonary arteries (arrowheads). It is important to be aware that the basilar segmental arteries are not “pruned,” but rather have a string-like appearance.


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pneumonia, pneumothorax, rib fractures, aortic dissection, pleural effusions, pericardial effusion, tumor, and hiatal hernia.

Nonspecifi c radiograph fi ndings in pulmonary embolic disease include an elevated hemidiaphragm, pleural effusion, and atelectasis.

Although most pulmonary emboli occur without chest x-ray fi ndings, three classic radiographic signs have been described for pulmonary embolic disease. These signs occur in fewer than 10% of patients with pulmonary emboli.18,19 The Hampton’s hump is a wedge-shaped pleural-based density representing a lung infarction secondary to an embolus. The Westermark sign is proximal pulmonary arterial dilatation and peripheral oligemia. The Fleischner sign is a large central pulmonary artery due to central thrombus with abrupt taper-ing. Helical CT is most accurate in detecting pulmonary emboli.

Septic pulmonary emboli manifest as multiple ill-defi ned wedge-shaped or round peripheral nodules on chest radio-graphs. These can be associated with infected central venous catheters, tricuspid valve endocarditis, or peripheral septic thrombophlebitis.

Pericardial Diseases

It is diffi cult to distinguish between cardiomegaly resulting from chamber dilatation and pericardial effusion on a chest x-ray, as the fi ndings are practically similar. An acute increase

in cardiac size on serial chest x-ray, a fl ask-shaped heart, and relatively clear lung fi elds would favor the diagnosis of peri-cardial effusion (Fig. 4.15). The presence of calcifi cation, par-ticularly ring-shaped calcifi cation, best visualized on the lateral view of a chest x-ray, would suggest the diagnosis of constrictive pericarditis. Epicardial fat and pericardial cysts could alter the cardiac silhouette by obscuring the diaphrag-matic angles.

Summary

Chest x-ray remains one of the oldest and most commonly used radiographic techniques. It can be used to diagnose cardiovascular conditions and assess the response to treat-ment. Appropriate image acquisition in conjunction with a systematic approach is essential for proper interpretation of a chest x-ray. A good inspiratory effort and an erect position are important determinants of a good-quality chest x-ray. Typically, the cardiac silhouette occupies about 45% of the widest chest diameter. An increase beyond 60% indicates left ventricular enlargement, at least by 66%. Enlargement of the right ventricle does not signifi cantly affect the cardio-thoracic ratio. Left atrial enlargement may be evident as widening or splaying the angle of carina as well as fullness and straightening of the left heart border. Chest x-ray fi nd-ings of cardiomegaly due to chamber enlargement and peri-cardial effusion are largely similar and not suffi ciently helpful in differentiating these two conditions.

FIGURE 4.15. PA (A) and lateral (B) chest x-ray in a patient with pericardial effusion.A B


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A chest x-ray is not suffi ciently sensitive or specifi c for the diagnosis of aortic dissection, which could be easily diagnosed by spiral CT. Chest x-ray is quite useful in the diagnosis of pulmonary congestion and could provide some evidence of left atrial pressure. An increased pulmonary artery pressure is diagnosed by pruning of the middle and distal pulmonary arteries and dilatation of the main pulmonary artery. A chest x-ray has a poor sensitivity and specifi city for the diagnosis of pulmonary embolism, a condition readily diagnosed by spiral CT pulmonary angiography.

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