Calcification can be present in many cardiac structures, including the pericardium, the cardiac valves, and the walls of the cardiac chambers, as well as in organized thrombus and in the coronary arteries due to atheroma. Aortic valve calcification can be seen on the lateral radiograph as a ring of calcification projected centrally over the heart (Fig. 6-4). The presence of aortic valve calcification implies stenosis. Mitral annular calcification is common in patients more than 70 years of age; it appears as a C-shaped ring near the posterior and inferior aspects of the heart on the lateral radiograph (Fig. 6-5). Mitral annular calcification does not imply functional impairment of the mitral valve. In contrast, calcification of the mitral leaflets is associated with rheumatic heart disease and usually indicates significant mitral valve dysfunction, usually stenosis. Mitral leaflet calcification is seen in the same region as annular calcification but is punctate and lacks the C-shape of the more benign annular calcification. The positions of each of the four heart valves on frontal and lateral radiographs are shown in Figure 6-6.

Figure 6.4 Lateral radiograph showing aortic valve calcification (arrows). See text for details.

Figure 6.5 Lateral radiograph showing mitral annular calcification (arrows). See text for details.

Figure 6.6 A and B, Frontal and lateral radiographs of a patient with four prosthetic heart valves. A mechanical prosthesis has been inserted in each of the four heart valve positions.

Hiatus Hernia

Hiatus hernia results in a retrocardiac mass that is predominantly left-sided but can bulge slightly to the right of the midline on a frontal radiograph. Such hernias are common and are best appreciated on an erect chest radiograph, on which they can usually be seen to contain an air fluid level. On a supine film, a hiatus hernia may be mistaken for a left basal pneumothorax.

Pulmonary Vascularity

Pulmonary Arterial Hypertension

Signs suggestive of pulmonary arterial hypertension include:

1. A diameter of the right descending pulmonary artery on a PA chest radiograph of more than 16 mm.

2. Right ventricular enlargement.

3. Peripheral pulmonary vascular attenuation with pruning of the proximal pulmonary arteries.

On thoracic CT, the signs of pulmonary arterial hypertension include a transverse diameter of the main pulmonary artery greater than that of the adjacent ascending aorta as well as the presence of pericardial fluid and minor pericardial thickening.¹

Pulmonary Venous Hypertension and Pulmonary Edema

Three changes in pulmonary vascularity occur in patients with raised left atrial pressure:

1. Pulmonary venous hypertension. In the erect chest film, pulmonary venous hypertension results in a progressive increase in the caliber of the vessels in the upper lobes. If vessels in the first anterior interspace have a caliber greater than 3 mm, it is suggestive of either pulmonary venous hypertension or plethora (e.g., due to left-to-right shunt). With pulmonary venous hypertension, the upper lobe vessels are larger than the lower lobe vessels, whereas the usual pattern of lower lobe dominance is maintained with plethora.

2. Interstitial edema. Increased interstitial fluid within the pulmonary parenchyma results in the thickening of the interlobular septa (Kerley A and B lines), in peribronchial thickening, and in fuzziness around vessels. Kerley B lines are seen as horizontal lines perpendicular to the chest wall peripherally, in the mid to lower zones, and measuring 1 to 3 mm in thickness (Fig. 6-7). Kerley A lines are thickened interlobular septa that are seen within the more central lung, passing obliquely toward the pulmonary hilum. Septal lines that persist beyond resolution of heart failure may occur due to hemosiderin or fibrin deposition within the septa.

3. Alveolar pulmonary edema. Alveolar filling by transudate results in a generalized increase in parenchymal density. Classically, this has a perihilar distribution and causes symmetric perihilar consolidation (the “bat-wing” pattern) (Fig. 6-8). Evidence of pulmonary venous hypertension and interstitial edema is usually obscured, but it becomes apparent as the alveolar edema subsides. Alveolar edema can be asymmetric, usually due to patient positioning or underlying lung pathology (e.g., bullous emphysema). Pulmonary venous obstruction is a rare cause of asymmetric alveolar edema.

Figure 6.7 Chest radiograph detail showing Kerley B lines (arrows). See text for details.

Figure 6.8 AP radiograph, patient erect, showing alveolar pulmonary edema. The perihilar and symmetric nature of the infiltrates favors a diagnosis of alveolar pulmonary edema over ARDS (see Fig. 6-17). Interstitial fluid, as demonstrated by the thickening of the horizontal fissure (arrow), can also be seen.

On a supine chest radiograph, the gravitational changes of pulmonary venous hypertension are not identified, but the signs of interstitial and alveolar edema are unchanged. Pleural fluid often coexists with interstitial or alveolar edema.

Chronic Obstructive Pulmonary Disease

Emphysema is associated with hyperinflation of the chest and peripheral pulmonary vascular attenuation. The signs of hyperinflation include inferior displacement of the hemidiaphragms below the sixth to seventh anterior ribs on an inspiratory film, flattening of the domes of the hemidiaphragms, and an increase in the retrosternal airspace on the lateral radiograph. Pulmonary vessels are thin and less profuse in areas of lung affected by emphysema. In centrilobular emphysema, the distribution of emphysema is predominately within the mid and upper zones. In panlobular emphysema, as seen in α-1 antitrypsin deficiency, the distribution is basal. Bullae can be identified on the chest radiograph in one third of patients with emphysema. When bullae are large they can be confused with pneumothoraces (see later discussion).

Bronchiectasis may be evident on the plain radiograph as dilated, nontapering airways with thickened walls, usually in the lower zones. The chest radiograph is commonly normal in patients with chronic bronchitis and asthma.

POSTOPERATIVE AND POSTPROCEDURE CHEST RADIOGRAPHS

An AP chest radiograph should be obtained in all patients once they arrive in the ICU after cardiac or thoracic surgery. A chest radiograph should also be obtained following all invasive thoracic procedures, such as the insertion of chest drains, central venous catheters, and endotracheal or tracheostomy tubes. In addition to the issues outlined earlier concerning the preoperative chest radiograph, certain issues are specific to the postoperative or postprocedure chest radiograph.

Lines and Tubes

The best positions for certain lines and tubes are shown in Figure 6-9.

Figure 6.9 Chest radiograph, patient supine, demonstrating multiple lines and tubes. An endotracheal tube (ETT), central venous line (CVL), pulmonary artery catheter (PAC), intraaortic balloon pump (IABP), along with three pleural drains (arrows) can be seen. The outline of the inflated IABP can be seen, which indicates that the radiograph has been taken during diastole. Sternal wires and clips on the internal mammary artery can be seen. In addition, there is left lower lobe collapse (see Fig. 6-16).

Endotracheal Tube

The ideal position for the tip of an endotracheal tube is in the midthoracic trachea, approximately 3 to 4 cm above the carina. Lower positions may result in the migration of the tube into the right main bronchus, and more proximal positions may result in accidental extubation, particularly with neck flexion. The carina lies at the level of the fifth or sixth thoracic vertebral body.²

Pleural and Mediastinal Drains

After cardiac surgery, it is usual to place a left-sided (and sometimes a right-sided) pleural tube as well as two mediastinal tubes from the substernal region. Mediastinal tubes may be rubber and are therefore not visualized on plain chest radiograph, but pleural tubes are usually plastic and have a marker that is visible on a chest radiograph.

After thoracic surgery, two pleural tubes are often placed, one apical and one basal. In the ICU, pleural tubes are also inserted for the treatment of pneumothorax or fluid collections.

Malposition of pleural drains is a common cause of patient morbidity. Emergently placed chest tubes are particularly prone to malposition; on CT scan review, as much as 26% of intercostal drains are found to have been misplaced. The most common misplacement is interfissural positioning.³ The interlobar fissures are commonly incomplete, and pulmonary lacerations with pneumothorax, hemothorax, or bronchopleural fistulae can result from such tube positions. A correctly placed pleural drain usually has a curved intrathoracic course, whereas an interfissural tube has a straight intrathoracic course, and the tube tip is directed at the pulmonary hilum.⁴ If there is doubt about the tube position it may be verified by thoracic CT scan.

Central Venous Catheters

The optimal position for a central venous catheter is for the tip of the catheter to be in the superior vena cava outside the pericardium above the superior vena cava/right atrial junction. A catheter within the right atrium may cause cardiac arrhythmias and, rarely, cardiac perforation. On frontal radiograph, the tip of the catheter should be above the level of the angle between the right main bronchus and the trachea.⁵ Central venous catheters that are kinked or have curved into the wall of a vein may also cause perforation and should be repositioned.

Pulmonary Artery Catheter

The optimal position of a pulmonary artery catheter is for the tip of the catheter to be within the left or right main pulmonary artery. The placement is identified on frontal chest radiograph by observing that the tip of the catheter is proximal to the edge of the pulmonary hilum. Placement of the catheter more peripherally increases the risk for pulmonary arterial perforation.

Intraaortic Balloon Pump

The optimal position of an intraaortic balloon pump is for the tip of the catheter to be at the level of the inferior margin of the aortic arch, as seen on the frontal radiograph. A catheter positioned more proximally may impede flow to the head and neck vessels or may directly traumatize the wall of the aorta. Catheters placed more distally in the descending aorta may extend to overlie the origins of the visceral vessels, potentially causing renal or splanchnic ischemia.

Nasogastric and Nasojejunal Tubes

The optimal position of a nasogastric tube is for the tip of the tube to lie in the body or antrum of the stomach. Tubes lying with their tips in the fundus of the stomach or at the gastroesophageal junction should be advanced.

A nasojejunal tube should lie with its tip in the proximal jejunum, just beyond the duodenojejunal flexure. Correct placement of a nasojejunal tube is identified by observation that the tube passes across the midline (from the patient’s left to right) and curls in a semicircle to lie with the tip back on the left of the patient’s midline (see Fig. 34-4). Occasionally, in a patient with marked gastric distension, the stomach may extend across the midline, making it difficult to be sure of correct placement. The position can be confirmed by fluoroscopic-contrast examination.

Mediastinum

Mediastinal Widening

Mediastinal widening is an almost universal finding following cardiac surgery. Widening of up to 50% from the preoperative PA chest film to the postoperative AP supine film is a normal finding. Mediastinal widening of 70% or more (Fig. 6-10) is indicative of mediastinal bleeding and is associated with an increased need for surgical reexploration.⁶ The differential diagnosis includes upper lobe collapse or consolidation.

Figure 6.10 Chest radiograph, patient supine, demonstrating mediastinal widening due to hemorrhage. This radiograph was taken several hours after cardiac surgery. The absence of volume loss and air bronchograms distinguishes this image from those showing left upper lobe collapse and consolidation, respectively.

Mediastinitis

The chest radiographs of patients with mediastinitis may demonstrate mediastinal widening and small pockets of mediastinal air, but these findings may also be present in patients without mediastinitis. Greater sensitivity and specificity for mediastinitis are obtained from a contrast-enhanced CT scan. The CT scan features that suggest mediastinal infection include:

• Increased mediastinal fat density (indicating edema in the mediastinal fat)

• Fluid collection seen with contrast enhancement of the wall of the collection.

• Gas within fluid collections (present more than 2 days postoperatively).

• Fluid collection deep to the sternum.

• Pericardial and pleural fluid.⁷

Pericardial Effusion

The AP chest radiograph has low sensitivity and specificity for determining the presence of hemodynamically significant pericardial collections in patients after cardiac surgery. Radiographic signs indicating the need for further investigation (usually with echocardiography) include a globular cardiac shadow and a significant increase in apparent cardiac size over a short time interval (Fig. 6-11, A and B).

Figure 6.11 A and B, Accumulation of pericardial fluid. These two AP radiographs, patient erect, were taken 24 hours apart and show a dramatic increase in the apparent size of the heart. Echocardiography confirmed the presence of a large collection of pericardial fluid.

Pulmonary Edema

At least 25% of patients who have undergone cardiopulmonary bypass show signs of pulmonary edema, usually interstitial edema, on the immediately postoperative chest radiograph (see earlier material). Reexpansion pulmonary edema is an uncommon complication of the rapid drainage of large pleural effusions or pneumothoraces.

Lung Collapse

Lobar collapse, particularly involving the left lower lobe, is extremely common following cardiac surgery. The collapse of an entire lung is usually caused by endobronchial placement of a tracheal tube; it usually involves the right main bronchus and causes collapse of the left lung.

Collapse is associated with signs of volume loss within the lung, including shift of the pulmonary fissures, crowding of the pulmonary vessels and bronchi, and shift of the hilum of the affected lung—either superiorly, in cases of upper lobe collapse, or inferiorly, in cases of lower lobe collapse. Increased density within the pulmonary parenchyma of the collapsed lobe or lung is also seen, and it may obscure vessels that would normally be visible (e.g., loss of visualization of the right lower lobe artery in cases of right lower lobe collapse).

An important sign that indicates collapse (or consolidation) of lung tissue is loss of the silhouette sign, in which aerated lung lying next to soft tissue structures enables visualization of these structures. For example, visualization of the apex of the heart is dependent on the presence of air within the lower left thorax—typically within the lingula. If the lingula is consolidated or collapsed, air is replaced by soft tissue density and the left cardiac apex becomes indistinct.

Outside of the collapsed lung or lobe, there may be other signs of volume loss. They include a shift of the mediastinum to the affected side, crowding of the ribs, and elevation of the hemidiaphragm. There may be compensatory hyperexpansion of other lobes of the affected lung. Specific patterns of collapse of different lobes are recognizable on a chest radiograph.

Right Upper Lobe Collapse

The right upper lobe (Fig. 6-12) collapses medially and the horizontal fissure swings superiorly, creating a well-demarcated density medially in the right upper thorax. The pulmonary hilum on the right is elevated. The trachea is deviated to the right. The right paratracheal stripe and superior vena cava are not visualized. Right upper lobe collapse may be mistaken for mediastinal hematoma, with volume loss tending to support the diagnosis of collapse. Right upper lobe collapse may occur in a ventilated patient due to obstruction by the endotracheal tube of a right upper lobe bronchus that originates in the distal trachea (a variant of normal anatomy).

Figure 6.12 Right upper lobe collapse. See text for details.

Right Middle Lobe Collapse

Right middle lobe collapse (Fig. 6-13) is more obvious on a lateral projection than a frontal image. The lobe collapses medially to lie adjacent to the right heart border, and this causes loss of definition of a portion of the right heart border. The horizontal fissure will not be visible. On the lateral projection there is a triangular density in the anterior inferior thorax with the apex pointing towards the hilum.

Figure 6.13 Right middle lobe collapse. See text for details.

Right Lower Lobe Collapse

The right lower lobe (Fig. 6-14) collapses medially, posteriorly, and inferiorly, creating a wedge of increased density in the right lower thorax. The right lower lobe pulmonary artery is not visualized because of the increased parenchymal density around it. The right hemidiaphragm may be raised, reflecting volume loss. The lateral projection demonstrates increased density overlying the lower vertebrae, and the right hemidiaphragm is obscured.

Figure 6.14 Right lower lobe collapse. See text for details.

Left Upper Lobe Collapse

The left upper lobe (Fig. 6-15) includes the lingula. This lobe collapses anteriorly and reveals no sharp interface on the frontal film; rather, a veiling density is seen over the left upper thorax because the aerated lower lobe is being seen through the collapsed upper lobe. The upper mediastinum and trachea are displaced to the left, and the left hilum is elevated. The left heart border is indistinct due to loss of air from the lingula. On the lateral radiograph, a dense vertical band of collapsed lung is seen anteriorly.

Figure 6.15 Left upper lobe collapse. See text for details.

Left Lower Lobe Collapse

The pattern of left lower lobe collapse (Fig. 6-16) mirrors that of the right lower lobe, but the features may be less readily appreciated because the left lower lobe is behind the density of the heart. On the frontal view there is a triangular density behind the heart combined with loss of visualization of the left lower lobe pulmonary artery, inferior displacement of the left hilum, and elevation of the left hemidiaphragm. The descending aorta is indistinct because of the dense lung adjacent to it. On the lateral projection there is increased density overlying the lower vertebrae and loss of the left hemidiaphragm.

Figure 6.16 Left lower lobe collapse. See text for details.

Multilobe Collapse

Typically, multilobe collapse affects the right middle and lower lobes because of obstruction of the bronchus intermedius. Collapse of these two lobes shows a combination of the patterns seen in the collapse of the individual lobes.

Differentiation of Lung Collapse from Consolidation

Many causes of pulmonary consolidation also cause a degree of collapse. Lobar pneumonia is typically associated with volume loss of about 25%. Volume loss of more than this would support predominant collapse over consolidation. Sometimes consolidation is associated with no volume loss or occasionally with lobar expansion, for example, in gram-negative pneumonia or proximal bronchial obstruction with fluid accumulation within the distal lung (drowned lung). The patterns of individual lobar or lung consolidation mirror those of collapse of the same lobes, although there is less evidence of volume loss. The presence of air bronchograms supports the diagnosis of consolidation over collapse.

Acute Respiratory Distress Syndrome

In the early stages of acute respiratory distress syndrome (ARDS), the chest radiograph may be normal or demonstrate only hazy pulmonary opacities. With time, the presentation progresses to patchy consolidation (Fig. 6-17). In a supine patient, consolidation is typically most extensive in the posterior and inferior aspects of the lower lobes. Pleural effusions and atelectasis are common.

Figure 6.17 Chest radiograph, patient supine, demonstrating acute respiratory distress syndrome (ARDS). Dense bilateral pulmonary infiltrates can be seen. The differential diagnosis includes pulmonary edema and pneumonia. The asymmetry of the infiltrates and the extension of the consolidation into the periphery of the lung favor a diagnosis of ARDS over pulmonary edema.

On plain radiography, it can be difficult to make the distinction between cardiogenic pulmonary edema and ARDS. In general, cardiogenic pulmonary edema demonstrates more interstitial thickening, whereas ARDS demonstrates more consolidation on air bronchograms. In cardiogenic pulmonary edema, the development of symptoms tends to mirror radiographic findings, whereas in ARDS, hypoxemia may precede radiographic abnormalities. CT scanning in ARDS demonstrates regions of consolidation, dependant atelectasis, and pleural fluid (see Fig. 27-2) and is useful for the detection of lung abscesses or small pneumothoraces.⁸

Pleural Effusion

Imaging findings in pleural effusion depend on the volume and consistency of the fluid, whether the fluid is free or loculated, and whether the film is exposed when the patient is erect or supine.

Chest Radiograph, Erect

Small volumes of free fluid result in a slight blunting of the lateral costophrenic angles associated with separation of the inferior and lateral lung from the adjacent costal margin. Fluid accumulates in the posterior costophrenic recess, obscuring vessels below the hemidiaphragm. As the volume of fluid increases, a fluid meniscus develops on the lateral chest wall (Fig. 6-18).

Figure 6.18 Chest radiograph, patient erect, demonstrating a left pleural effusion. A density is seen in the left lower zone, with separation of the apparent left hemidiaphragm from the stomach bubble (arrow).

Large quantities of pleural fluid may occasionally collect under the lung and not track up the lateral chest wall. This is termed subpulmonic effusion (Fig. 6-19). The chest radiograph demonstrates apparent elevation and lateral tenting of the hemidiaphragm. On the left, a subpulmonic effusion can be differentiated from elevation of the hemidiaphragm by the separation of the apparent diaphragm from the gastric air bubble.

Figure 6.19 PA chest radiograph, patient erect, demonstrating subpulmonic fluid. On the right, the fluid has resulted in lateral tenting (arrow) of the apparent right hemidiaphragm.

Although plain radiography is not an accurate method for assessing the volume of pleural fluid, it does give a rough indication: the presence of a visible fluid meniscus implies 150 to 200 ml of fluid; elevation of the lung base implies 400 to 800 ml; fluid at the level of the mid thorax is indicative of 1000 to 1500 ml or more. A very large pleural effusion may cause an opaque hemithorax.

Loculated pleural effusions exist when pleural fluid collects between the layers of visceral pleural in the fissures or when fluid accumulates between focally adherent layers of parietal and visceral pleura. Interfissural collections are typically lenticular in shape when viewed from the side but may appear round when viewed en face.

Chest Radiograph, Supine

On a chest radiograph taken when the patient is supine, free fluid pools posteriorly in the thorax and creates a veiling density over the hemithorax (Fig. 6-20). The persistent visualization of pulmonary vessels is suggestive of the extrapulmonary nature of the increased density. A pleural cap may be evident at the apex of the lung. The perception of pleural fluid is reduced when the patient is supine, and large effusions may not be recognized.

Figure 6.20 Chest radiograph, patient supine, showing a right pleural fluid collection. A veiling density can be seen over the hemithorax. Fluid can also be seen in the horizontal fissure. An aortic prosthetic valve and mitral and tricuspid annuloplasty bands are also seen. Other standard postoperative lines and tubes are also present (see Fig. 6-9).

Ultrasound Imaging

The sonographic characteristics of fluid vary according to the nature of the fluid. Transudates typically appear as echo-free collections, whereas exudates are more echogenic because of the presence of particles in the fluid, and they may have organizing fibrin within them that appears as multiple septations. Hemothoraces may have a mixture of both appearances.

The sonographic estimation of fluid volume is most accurate when the patient is scanned from the back while seated erectly because fluid collects in the posterior costophrenic recess. Alternatively, in the ICU, bedside fluid volume may be estimated with the patient semireclined or in a partial decubitus position, but these positions are less accurate for evaluating small effusions. Draining a collection is facilitated by marking the skin at an appropriate site or by real-time ultrasound-guided placement of a pleural tube. Ultrasound imaging has a tendency to underestimate the volume of fluid. Interfissural collections may not be apparent because ultrasound is unable to image through air to reveal the fluid collection. Ultrasound imaging is highly operator-dependent, and images are prone to being misinterpreted by inexperienced observers.⁹

Computed Tomography Scanning

CT scanning is the most sensitive and specific means of demonstrating pleural fluid and is the imaging modality of choice for complex pleural fluid collections. The morphology of the fluid collection can provide important clues about whether the fluid is free or loculated. Free fluid tends to layer in a dependent fashion. Pleural thickening suggests a diagnosis of empyema, particularly if there is pleural enhancement with contrast or if there are signs of edema in the chest wall.¹⁰ CT scanning may not be able to identify septations within fluid collections that can impede percutaneous drainage; septations are best assessed by ultrasound imaging.

Causes of Pleural Effusions in the Cardiothoracic ICU

Left-sided pleural effusions are common following coronary artery bypass graft surgery. Their occurrence has been attributed to a combination of heart failure and impaired pleural fluid clearance resulting from dissection of the internal mammary artery and pleurotomy.¹¹

Heart failure and iatrogenic fluid overload are common causes of bilateral pleural effusions. Right-sided effusions tend to be slightly larger than left-sided effusions.

Rare causes of pleural effusions include:

• Postcardiac injury syndrome. This is a clinical syndrome that includes pleuritis, pneumonitis, and pericarditis; it occurs after a variety of myocardial and pericardial injuries. The prevalence is higher following cardiac surgery (about 5%) than following myocardial infarction. Pleural effusions are common and may arise anywhere from 2 to 86 days after the injury; the average is 20 days.¹²

• Chylothorax. The thoracic duct is closely related to the aortic arch and mid esophagus. Surgery involving these structures is the most common surgical cause of chylothorax. The density of the effusion is usually higher than that of fat because of the protein in the fluid.

• Pulmonary embolism. Unilateral pleural effusions can be seen in 30% to 50% of people with pulmonary embolism. Effusions are typically hemorrhagic and small.

• Peritoneal dialysis. Ascites and peritoneal dialysis can result in pleural effusions; they commonly affect the right side.

Differentiation of Lower Lobe Collapse From Pleural Fluid

On an erect frontal radiograph, both lower lobe collapse and pleural effusion cause increased density in the lower thorax. Differentiation may be difficult, and both processes may be present in the same patient. Signs of volume loss within the suspect lobe indicate predominant collapse as opposed to pleural fluid. For example, if the right lower lobe pulmonary artery is still visible, the increased density in the right lower thorax is more likely to be caused by fluid than is right lower lobe collapse. If there is continuing doubt, ultrasound or CT scanning is indicated.

Pneumothorax

Pneumothoraces are common in the cardiothoracic ICU and may be discovered incidentally on routine postoperative chest radiographs. Small pneumothoraces are easily missed, both clinically and radiographically. The appearances of a pneumothorax are strongly influenced by the darkness or lightness of the film and whether the radiograph is taken when the patient is in the supine or the erect position.

Chest Radiograph, Erect

When a patient is erect, a film shows air rising in the pleural space and separating the lung from the chest wall, particularly at the lung apex (Fig. 6-21). Films taken on expiration do not convincingly increase the pickup rate for pneumothorax.¹³ False-positives for pneumothorax can occur because of any linear density overlying the apex and lateral aspect of the thorax, particularly overlying skin folds (Fig. 6-22), but also vascular catheters, hair, clothing, and bedding. Skin folds are a common finding in the AP chest radiographs of elderly patients because redundant skin is compressed by the radiographic plate. Skin folds may extend outside of the confines of the thoracic cavity, and lung markings may be visible lateral to the line of the fold. If there is confusion about the presence of a pneumothorax or an artifact, the patient should be repositioned and a repeat radiograph should be performed.

Figure 6.21 AP chest radiograph, patient erect, showing bilateral pneumothoraces. The lung edges (arrows) are quite subtle but can be identified.

Figure 6.22 Chest radiograph, patient supine, showing a skin fold. Pulmonary vessels can be seen beyond the apparent lung edge, confirming the absence of a pneumothorax. A tracheostomy tube and a gastric tube are also present. The lungs show pulmonary edema.

Bullae can be difficult to distinguish from pneumothoraces. Bullae are limited to an anatomic lobe of the lung and do not adopt the shape of the pleural space. Review of old radiographs may be helpful. CT scanning can differentiate a pneumothorax from a bulla by demonstrating the internal structure within the airspace of a bulla and the visceral pleura around a pneumothorax.¹⁴ Bullae tend to be oval-shaped (Fig. 6-23), whereas pneumothoraces are typically lens-shaped.

Figure 6.23 CT scan showing a bullous airspace (arrow). The rounded shape is indicative of a bulla rather than a pneumothorax.

In a tension pneumothorax, the volume of the pneumothorax is usually large and there are signs of mediastinal displacement, diaphragm flattening, and ipsilateral lung collapse. Dynamic hyperinflation following single-lung transplantation can be mistaken for a pneumothorax (see Fig. 13-2). Collapse or fluid on the contralateral side can also give the impression of a pneumothorax.

Chest Radiograph, Supine

Pleural gas collects in the highest part of the thorax which, when the patient is in the supine position, is the anterior costophrenic recess (i.e., at the lung base). Depending on the size of the pneumothorax, the lung may not appear to be separated from the chest wall. Radiographic signs of a pneuomothorax in the supine patient are:

1. Decreased density of all or a significant portion of the hemithorax.

2. Increased sharpness of the mediastinal border, with the lung’s edge sitting next to the mediastinal margin as a result of free air.

3. Extension of air into the anterior costophrenic sulcus, resulting in visualization of this sulcus that is usually obscured by the hemidiaphragm. This is termed the deep sulcus sign (Fig. 6-24).¹⁵

4. Visualization of air underneath the lung base. This must be differentiated from a pneumoperitoneum.

5. Depression of the hemidiaphragm in instances of tension associated with pneumothorax on a film taken when the patient is in the supine position.

Figure 6.24 Supine chest radiograph showing the deep sulcus sign indicative of a pneumothorax. See text for details.

If there is doubt regarding the presence of a pneumothorax and it is not possible to take a radiograph when the patient is in an erect position, a film of the patient in the decubitus position with the suspicious side upward can show air tracking along the lateral chest wall. Alternatively, a CT scan of the thorax will confirm the diagnosis and also guide the placement of a chest tube.

Bronchopleural Fistula

A direct communication between an airway and the pleural space is called a bronchopleural fistula. After pneumonectomy, the presence of a bronchopleural fistula is suggested by a decrease in the volume of fluid and an increase in the volume of air in the post-pneumonectomy space (see Fig. 12-6). There may be changes of pneumonia on the contralateral side as a consequence of aspiration. The volume of the affected hemithorax may increase, as demonstrated by a shift of the mediastinum toward the contralateral side, reversing a trend toward reduced volume on the operated side. CT scanning with fine slices and multiplanar reconstructions may identify the site of the fistula.¹⁶

Chest Wall and Diaphragm

Sternum

On the chest radiograph, sternal dehiscence is seen as disruption of or alteration in the orientation of the sternal wires and a widening of the junction line between the two sternal halves. Dehiscence is often accompanied by sternal infection. On CT, sternal osteomyelitis results in sternal destruction and fluid collections around the sternum or between the two halves of the sternotomy.¹⁷

Diaphragm

Impaired diaphragmatic function due to phrenic nerve injury is common following cardiac surgery. The left hemidiaphragm is the most commonly affected. On a plain radiograph, phrenic nerve paresis is revealed by a raised hemidiaphragm, which commonly becomes apparent after extubation (Fig. 6-25, A and B). Phrenic nerve injury can cause, and also be mistaken for, lower lobe atelectasis. In nonventilated patients, diaphragmatic motion can be assessed at the bedside by ultrasound imaging. Motion is graded as being normal, reduced, absent, or paradoxic. There is strong agreement between absent and paradoxic diaphragmatic motion and impaired phrenic nerve conduction with electrophysiologic testing. Most phrenic nerve injuries that occur as a consequence of cardiac surgery have resolved after 12 months.¹⁸

Figure 6.25 Diaphragmatic paresis. A, Radiograph was obtained while the patient was mechanically ventilated and shows no diaphragmatic abnormality. B, Radiograph was taken after extubation and shows elevation of the left hemidiaphragm. Paradoxic motion of the diaphragm was confirmed by ultrasound imaging.

Figure 6.26 Massive pleural collection. The absence of volume loss or mediastinal shift toward the affected side suggests a pleural collection rather than collapse.

Subdiaphragmatic Air

Subdiaphragmatic air is common following cardiac surgery; it occurs as the result of opening the peritoneal space at the inferior extent of the median sternotomy or during placement of mediastinal and pleural drains. Usually, only small volumes of air are introduced and they escape detection on a chest radiograph taken when a patient is in the supine position, becoming evident only when the first image is obtained in a patient who is erect. Following laparotomy, pneumoperitoneum may persist for more than 2 weeks.¹⁹ An increased volume of free air revealed by consecutive radiographs raises the possibility of perforated abdominal viscus and warrants further investigation. If a perforated viscus is suspected and the patient cannot sit up, a plain abdominal radiograph may be obtained when the patient has been placed in a right-sided decubitus position. CT scanning is indicated if further radiologic investigation is required.

SICK PATIENT WITH AN ABNORMAL CHEST RADIOGRAPH

Three important abnormalities viewed on chest radiographs demand immediate attention. The abnormalities and possible diagnoses are outlined in Table 6-1.

Table 6-1 Critical Abnormalities on Chest Radiographs and Possible Causes

Abnormality	Possible Causes
Whiteout hemithorax (Fig. 6-26)	Massive hemothorax or pleural collection
	There is no volume loss; there may be volume gain.
	There may be signs of tension, including flattening and eversion of the hemidiaphragm and displacement of the heart and mediastinum to the contralateral side.
	Lung collapse
	It is often but not always caused by endobronchial intubation.
	The position of the endotracheal tube should be checked.
	There may be volume loss, with mediastinal shift toward the affected side.
Lucent hemithorax (Fig. 13-2A)	Large pneumothorax or tension pneumothorax
	There may be signs of tension, with mediastinal shift away from the affected side.
	Unilateral dynamic hyperinflation after single lung transplantation.
	Collapse or pleural fluid on the contralateral side.
Very wide mediastinum (Fig. 6-10)	Postoperative hemorrhage, particularly involving the internal mammary artery bed.
	There may be pericardial effusion.
	There may be a central venous catheter accident.