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RADIOLOGY OF THE CHEST METHODS OF EXAMINATION 1. Plain Film – The plain chest film is the most common imaging procedure ordered by the clinician. The routine chest exam consists of PA and lateral views. Other plain films are: AP, decubitus, lordotic, and oblique views (RAO, LAO, RPO, and LPO). 2. CT Scanning – CT scanning is helpful in the evaluation of many conditions involving the chest. It is particularly helpful in the evaluation of mediastinal mass lesions and in identifying normal structures such as vessels in the mediastinum, which may be mistaken for abnormalities on plain films. CT scanning of the lungs is useful in the evaluation of numerous conditions including: carcinoma, occult metastatic lesions, interstitial lung disease, bronchiestasis, and pleural abnormalities including pleural fluid and emphyema. CT scanning for the evaluation of pulmonary embolus has now become routine for the evaluation of PE and has largely replaced nuclear medicine and pulmonary angiography. CT scanning of the chest must follow a protocol tailored for the evaluation of a specific problem such as pulmonary embolus or interstitial lung disease 3. Angiography a. Pulmonary angiography – Has been the gold standard for the diagnosis of pulmonary embolus but has more recently been largely replaced by CT scanning. Angiography may be helpful in the evaluation of vascular lesions such as pulmonary AV malformations. b. Thoracic aortography – Helpful in distinguishing vascular lesions of the mediastinum such as aneurysms, pseudocoarctation, traumatic rupture of the aorta, etc. 4. Nuclear Scanning – helpful in the diagnosis of pulmonary embolus. 5. MRI – has a limited role in the evaluation of the chest. It may be useful in the evaluation of mediastinal abnormalities and the heart. PLAIN FILM VIEWS 1. PA – posterior anterior. This view is usually obtained at a 6 foot target to film distance in order to reduce magnification. With this view, the film is against the anterior aspect of the patient and the x-ray beam is directed toward the posterior aspect of the patient. 2. Lateral – a view of the patient’s sagittal plane. 1 3. AP – anterior posterior. The film is against the posterior aspects of the patient and the x-ray beam is directed toward the anterior aspect of the chest. This is the view commonly obtained with portable technique and the target to film distance is usually 40 inches. The cardiac silhouette is magnified in this projection. 4. Decubitus View - This film is obtained with the patient on the side and is named for the side which is down. The projection is usually obtained to evaluate for pleural fluid. 5. Oblique View – The oblique projections are the RAO and LAO. They are not usually obtained as a matter of routine but may be helpful in localization of an abnormality in the lungs and helpful in evaluation of the heart to determine specific chamber enlargement. 6. Lordotic View – This view is usually obtained in the AP projection with the patients tilted back. The clavicles are projected above the lungs, therefore, providing a better view of the upper lung fields. EVALUATION OF THE CHEST It is essential to have a systematic approach to the evaluation of the chest x-ray. The PA chest film should be well centered. This can be determined by checking the distance between the heads of the clavicles and the spinous process of the vertebra between the clavicles. The chest film should be penetrated just enough to see the thoracic vertebral bodies but not enough to see the intervertebral disc spaces. Films should be obtained in the best inspiratory effort possible. If nine of ten posterior ribs can be counted above the diaphragm, this usually means the film was obtained in good inspiration. It is important to recognize the normal before the abnormal can be appreciated. Several important features should be observed in analyzing the chest film: 1. The soft tissues and bony structures should be evaluated and checked for symmetry. 2. The right hemidiaphragm is usually slightly higher than the left. 2 3. The left hilus is slightly higher than the right. 4. The trachea should be in the midline position down to the aortic knob where there is slight deviation to the right by the aortic knob. 5. Observe the interlobar fissures. The minor fissure can be seen on the PA view running horizontally in the right mid lung field toward the hilus. The major fissures are usually not seen on the PA view, but can be well seen on the lateral view running from the anterior costophrenic angle to the region of the T-5 vertebral body. 6. On the lateral view, the thoracic vertebral bodies become more lucent (darker) as you go inferiorly. If they are more dense, this usually indicates an opacity in the posterior lung base. 7. Check the normal bumps along the mediastinum. On the left from superiorly to inferiorly are the left subclavian vessels, aortic knob, main pulmonary artery segment, left atrial appendage, and left ventricle. On the right are the innominate vessel, superior vena cava, right atrium, and inferior vena cava. 8. On the lateral view the right hemidiaphragm can usually be distinguished from the left because is extends all the way to the anterior chest whereas the left is obliterated anteriorly by the positive silhouette sign produced by the heart. The right hemidiaphragm is also slightly higher and the stomach bubble is under the left diaphragm. 9. The CP angles should be sharp. Blunting may indicate pleural effusion. 10. The vessels in the suprahilar region are smaller than those in the infrahilar region in the upright position. If the upper lobe vessels are the same size or larger than the lower lobe vessels, this usually means pulmonary venous congestion, possibly from left heart failure. On films obtained in the supine position, the upper lobe and lower lobe vessels are of equal size. 11. The stomach bubble is located approximately 5mm. below the left hemidiaphragm. If this distance is increased, pleural effusion should be suspected. If air is within 1mm. To 2mm. Under the diaphragm, free intraperitoneal air should be suspected. Free intraperitoneal air is usually located under the most superior aspect of the diaphragm. 12. Always look carefully behind the heart, in the CP angles and in the lung apices because pathology is frequently overlooked in these areas. 3 ABNORMALITIES PRODUCING INCREASED DENSITY IN THE LUNGS 1. 2. 3. 4. 1. Parenchymal disease a. Air space disease – consolidation b. Interstitial disease. Atelectasis Pleural effusion Pulmonary nodules and other mass lesions Parenchymal disease In general, these densities may be thought of as involving the air spaces, the interstitium of the lung or a combination of the two. A. Air space disease Fluid (exudates, transudate, blood) replaces the air in the pulmonary acinus. The pulmonary acinus represents that portion of lung to a terminal bronchiole and consists of respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. The acinus is the unit of lung that can be seen on the x-ray with air space disease as flurry irregular shadows approximately 5mm. in diameter. Air space disease may spread through the pores of Kohn and coalesce to produce consolidation. Air spaces and distal bronchial structures within an area of consolidation, which still contain air rather than fluid are identified as air bronchograms and are the hallmark of air space disease. Most pneumonias are manifest as air space disease. It is helpful to look for the distribution in the lung, pneumatoceles, pleural effusion, and other associated findings, which may help identify the specific type of pneumonia. Determination of a specific causative agent for pneumonia is usually not possible by x-ray. Pulmonary edema from any cause such as heart failure, azotemia, inhalation of noxious agents, etc. are manifest as air space disease in a perihilar or bat-wing distribution. Pulmonary hemorrhage may also have the same perihilar distribution. B. Interstitial disease The radiographic appearance of interstitial disease consists of either a nodular or reticular pattern. The nodules are usually small and punctate in appearance and the reticular pattern has the appearance of numerous interlacing linear densities. 4 Honeycombing may be associated with interstitial disease and appears as small cystic spaces within a coarse reticular infiltrate. Several diseases present with interstitial involvement. Interstitial edema secondary to congestive failure is one of the most common interstitial processes. Certain pneumonias may present as interstitial disease such as viral, Mycoplasma, and pnemocystics carinii infections. Many pneumonias represent a combination of interstitial and air space disease. Interstitial pneumonias in children, especially RSV pneumonias, also produce peribronchial thickening best seen in the hilar areas as peribronchial cuffing. CT scanning using a special technique of High Resolution , HRCT, is very helpful in the evaluation of diffuse parenchymal disease and permits the visualization of the parenchymal network of the lung. The interstitial network is much better seen than with the plain film or conventional CT. Thickening of the interstitial tissue from inflammation, fibrosis and tumor as well as focal areas of decreased opacity may be better appreciated with HRCT. There are a number of diseases which present primarily as diffuse interstitial disease. 1. 2. 3. 4. 5. 6. 2. Idiopathic interstitial fibrosis Sarcoidosis Rheumatoid lung Eosinophilic granuloma of lung Pneumoconiosis Metastatic disease Atelectasis – Volume loss in the lung may be secondary to obstruction of the bronchus, compression of lung tissue or scarring. Obstructive atelectasis is also known as resorption atelectasis. A major bronchus is occluded and there is a resultant resorption of air in spaces and loss of volume. Compression of lung may be secondary to an adjacent mass or bulla. Compression of lung by pneumothorax or effusion in the pleural space also results in loss in volume of the lung. Scarring may result in retraction and loss of volume. The signs of atelectasis are largely produces as a result of volume loss. 5 Signs of atelectasis: A. Local increased density B. Displacement of interlobar fissures C. Elevation of hemidiaphragm D. Displacement of mediastinum E. Compensatory overinflation F. Displacement of hila G. Approximation of ribs H. Absence of air bronchograms in obstructive atelectasis Displacement of fissures is one of the most important of the signs of atelectasis. The fissures always appear as sharp straight lines bordering on an area of increased density. 3. Pleural Effusion Pleural effusion is first seen in the posterior costophrenic gutters on the lateral view. The posterior gutter is deeper than the lateral costophrenic angles; therefore, small amounts of fluid are first seen here. The diaphragm on the side of the effusions is usually obliterated on the lateral view. Fluid then fills the lateral costophrenic angle. As fluid accumulates, the superior border appears as a meniscus. The lateral margin seems higher on the PA view because the x-ray beam is shooting through a greater thickness of fluid projection. The fluid appears to extend more posteriorly and anteriorly on the lateral view for the same reason. Occasionally, fluid may appear as an elevated diaphragm. This is referred to as subpulmonic effusion and the lung appears to elevate away from the diaphragm with the superior margin of the pleural fluid maintaining the same configuration as the diaphragm rather than a meniscus appearance. If pleural effusion is suspected, the decubitus view is the recommended view for further evaluation. This will reveal a shift and layering of fluid along the dependent portion of the chest is the fluid is free in the pleural space. Large amounts of pleural effusion may produce shift of the mediastinal structures to the opposite side. Fluid may also encapsulate in the pleural space if there is fusion on the parietal and visceral layers. The fluid in this case will demonstrate the 6 extrapleural sign with a convex border. This configuration is commonly seen with empyema and is best evaluated with CT scanning. CT scanning is also helpful to differentiate pleural fluid from other causes of parenchymal opacification. Fluid may also accumulate in an interlobar fissure and present as a homogeneous mass. The mass of elliptical configuration and conforms to an interlobar fissure. This is commonly seen with congestive failure. 4. Nodules and Mass Lesions Lung abscesses and loculated fluid may present as mass lesions. Malignancy should be the primary consideration in any mass that is encountered in the lung. Pulmonary nodules and other mass lesions should be carefully evaluated to determine if the lesion is single or multiple. CT is usually necessary to characterize the nodule and to determine if the nodule is single or multiple Other factors to be considered in evaluating a nodule are: A. Presence of calcifications – Central calcification indicates a benign lesion and is the only absolutely certain sign of benignity. Popcorn type calcification is characteristic of a hamartoma. B. Borders of the lesions – Smooth borders usually indicate a benign lesion; irregular and speculated margins indicate malignancy. C. Length of time the lesion has been present – If present for over two years with no change in size, this usually means a benign nodule; however, occasionally malignancy will go for ling periods without change. D. Location – Pulmonary sequestration may present as a mass and it typically located in the lung bases adjacent to the diaphragm. Metastatic lesions are more common in the lower lobes. It is unusual to find a solitary metastasis in the upper lobes. E. Cavitation – If the cavity wall is thick and irregular, lung abscess or carcinoma, either primary or metastatic, should be considered. If the wall is thin, this is usually a benign process such as a coccidioidomycosis or infected bulla. 7 F. Adjacent Structures – Pulmonary AV malformations characteristically have large vessels associated with the mass, which are directed toward the hilus. ABNORMALITIES WHICH PRODUCE DECREASED DENSITY OF LUNG Hyperinflation of the lungs from any cause will cause hyperlucency. Decrease in the pulmonary vascularity such as with congenital heart disease can cause generalized decreases density. CAUSES OF GENERALIZED RADIOLUCENCY OR HYPEREXPANDED LUNGS 1. 2. 3. 4. 5. 1. Emphysema Asthma Bronchiolitis Congenital heart disease Tracheal or laryngeal obstruction Emphysema – There is a pathological enlargement of the distal air spaces either from chronic dilation or from destruction of their walls. Radiographic features of emphysema: A. Lungs are hyperexpanded. The diaphragms are flattened and usually eleven posterior ribs can be seen on the PA view. The retrosternal space is increased. B. There is a reduction in the number and size of vessels in the peripheral portions of the lungs. C. The main pulmonary arteries are enlarged and the branches taper rapidly and there is reduction in the branching (pruning). This finding usually indicates pulmonary hypertension. D. The heart shadow usually appears long and narrow. 2. Asthma – the lungs are hyperexpanded with the diaphragm is a low position and there is increase in the retrosternal space. In contrast to emphysema, the vascular markings are usually normal. It is important to look for associated problems such as consolidation, atelectasis, pneumomediastinum and pneumothorax. 8 DECREASED DENSITY OF THE LUNGS MAY BE UNILATERAL IN WHICH CASE THE FOLLOWING CAUSES SHOULD BE CONSIDERED 1. Absence of soft tissues of the chest wall 2. Rotation – technical factors 3. Pneumothorax 4. Bullous emphysema 5. Compensatory overdistention with collapse 6. Absent of phypoplastic pulmonary artery 7. Congenital lobar emphysema 8. Pneumatocele 9. Pulmonary embolus Absence of soft tissues – Absence of soft tissues from mastectomy is one of the most common causes of one lung appearing more lucent than the other. Rotation – Rotation of the patient may produce a similar appearance. Pneumothorax – is a collection of air within the pleural space, between the visceral and parietal pleura. Pneumothorax may be spontaneous and is commonly produced by a ruptured bleb. Spontaneous pneumothorax may occur in young adults. Pneumothorax may be produced by many other conditions including interstitial lung disease and mechanical ventilation. Chronic obstructive pulmonary disease and asthma may also produce pneumothorax and be related to alveolar rupture with dissection into the pleural space. Alveolar rupture commonly dissects along vascular sheaths into the mediastinum and produces pneumomediastinum. Trauma is a common cause of pneumothorax and results from penetrating injury of the chest. Penetrating injury or rib fractures may rupture the pleura and result in pneumothorax. Pneumothorax may be iatrogenic following a thoracentesis or subclavian puncture for placement of subclavian lines. Radiographically, pneumothorax presents as a radiolucency of the chest due to the accumulation of air within the pleural space. No vascular markings are identified within the hyperlucent area. The hallmark of pneumothorax is the detection of the visceral pleural line profiled against air in the pleural space and air in the adjacent partially collapsed lung. There is radiolucency peripheral to the visceral pleural line, which represents air between the visceral and parietal pleura of the lung. Pneumothorax may be under tension in which case there is increased volume in the hemothorax with contralateral shift of the heart and mediastinum, depression of the diaphragm, and separation of the intercostal spaces. 9 A small pneumothorax may be very subtle and difficult to identify on the plain chest film. A film in expiration will accentuate the air within the pleural space and help in diagnosing a pneumothorax. Decubitus views and lateral projections are often helpful in identifying air within the pleural space. Bulla – An air-filled thin-walled space within the lung secondary to the destruction of alveolar tissue. A bulla is usually larger than 0.5 cm. and may become enormous in size compression adjacent lung tissue. A large bulla produces radiolucency or decreased density of the involved area. Bulla should be distinguished from blebs which are much smaller. Blebs – are air spaces usually less than 0.5 cm. in size located in the apical regions between the visceral and parietal pleura. Rupture of a bleb is commonly associated with spontaneous pneumothorax. Compensatory Emphysema – When a section of lung contracts, either by collapse or fibrosis or is surgically removed, the remainder of that lung expands by overinflation. Congenital Lobar Emphysema – occurs in infancy and may be a cause of respiratory distress. The upper lobes are the most commonly involved; sometime the right middle lobe. Congenital lobar emphysema is thought to be related to maldevelopment of cartilage in the bronchus producing air trapping. Radiographically, the lesion appears as an overdistended upper lobe, which is markedly hyperlucent and void of normal vascular markings. The mediastinum is frequently shifted to the opposite side, Pneumatocele – a thin-walled cystic structure similar in appearance to a bulla. These are probably secondary to overdistention and air trapping distal to a partially obstructed small bronchiole. They are commonly seen in staphylococcal and hydrocarbon pneumonias. Pulmonary Embolus – Radiographic findings in pulmonary embolus on the plain chest film are minimal and a normal chest film is frequently the case. An area of radiloucency or decreased density may be seen on the plain film as a result of the oligemia produced by the occluded pulmonary vessel. This area of radiolucency is know as the Westermark Sign. In pulmonary infarction, an area of pleural-based consolidation may develop in a segmental of subsegmental distribution. The pleural based density has a rounded configuration and is referred to as a Hampton’s Hump. Subsegmental atelectasis and pleural reaction with a small effusion are other common manifestations of infarction. The diaphragm may also be elevated on the affected side. Occasionally infarcts may become infected and cavitate. 10 The diaphragm may also be elevated on the affected side. CT scanning utilizing a special protocol to assure the proper timing of contrast media filling the pulmonary vessels is now the imaging method of choice CAVITIES Cavities represent a combination of increased and decreased density on radiographs and the following should be considered in the differential diagnosis of a solitary cavitary lesion. 1. Abscess 2. Bronchogenic carcinoma 3. Granulomas due to TB, fungus, or idiopathic 4. Metastatic neoplasms 5. Blebs or bullae 6. Lung cyst (bronchogenic, congenital) 7. Traumatic cyst 8. Pneumatocele In the cavity, the central portion of an area of increased density had been replaced by air. An abscess and cavity are not synonymous. An abscess which does not communicate with the bronchial tree is a homogeneous density on the radiograph. When necrotic tissue in the center of an abscess is replaced by air as a result of communication with the bronchus, it then becomes a cavity. Several features of a cavitary lesion should be carefully observed to help in the differential diagnosis. 1. Thickness of wall – A thick wall usually means lung abscess, primary or metastatic neoplasm. Thin walls may be seen in bullae, pneumatoceles, and post-traumatic lung cysts. 2. Inner lining – Irregular nodular inner lining usually means a carcinoma. A shaggy inner lining usually indicates a lung abscess. 3. Contents of a cavity – An intercavitary mass is diagnostic of fungus ball or mycetoma. This mass is frequently movable. A ruptured Echinococcus cyst may reveal the collapsed membrane floating on fluid within the cyst. 11 4. Multiplicity of lesions – Some cavitary lesions may be multiple and the following possibilities should be considered: A. Bullae B. Cystic bronchiectasis C. TB and fungus disease D. Metastasis E. Pneumatoceles F. Septic emboli G. Rheumatoid granulomas H. Wegener’s granulomatosis I. Cystic adenomatoid lung MEDIASTINAL LESIONS The divisions of the mediastinum as defined by the anatomist are difficult to identify on the radiograph. Because of ease in identifying the mediastinal compartments, the following radiographic subdivision is recommended as suggested by Felson. An imaginary line is traced upward from the diaphragm along the back of the heart and in front of the trachea to the neck. This divides the anterior from the middle mediastinum. A second imaginary vertical line connects the point of each thoracic vertebra 1 cm. behind its anterior margin. This divides the middle from the posterior mediastinum. Divisions of the mediastinum into the various compartments is helpful in differential diagnosis. 1. Anterior mediastinum a. Substernal thyroid b. Thymic lesions c. Teratomas d. Lymphoma ) ) ) ) 3 T’s and an L 2. Middle mediastinum a. Lymph node disease – inflammatory, primary, or metastatic carcinoma b. Bronchogenic cyst c. Esophageal lesions d. Aneurysms of aorta 3. Posterior mediastinum Neurogenic tumors 12 Thymomas are the most frequently found tumors of the anterior mediastinum and teratomas are a close second. Fifteen percent of patients with myasthenia gravis have thymomas. Seventy-five percent of thymoma patients have myasthenia gravis. Calcium may be present in either teratomas or thymomas. Presence of bone, teeth, or calcium in mediastinal teratomas is less common than in ovarian teratomas. Substernal thyroid commonly produces deviation of the trachea. Isotopic scanning is helpful in establishing the diagnosis of substernal thyroid. Bronchogenic cysts are usually found in the middle mediastinum and are commonly subcarinal in location. Gastroenteric cysts may be found in the middle mediastinum and are similar to bronchogenic cysts except that they are lined with GI mucosa and have two layers of muscle but no cartilage in the wall. They are usually closely associated with the esophagus. Lesions of the posterior mediastinum are almost always of neurogenic origin and common lesions are: 1. Neurilemomas – found in older people and have a rounded configuration 2. Ganglioneuromas – found in young people and are elliptical or fusiform in shape. 3. Neuroblastoma – a highly malignant tumor found in infants CONGESTIVE HEART FAILURE Congestive heart failure occurs when the left ventricle fails to eject a normal volume of blood during systole. Decreased ejection results in increased ventricular end-diastolic volume, increased pressure, and slight cardiac enlargement. Mild to moderate cardiac enlargement may not be detected on portable radiographs because of the magnification. Serial films showing progressive enlargement may be helpful. Because of the variability of heart size, radiographic signs of increased pulmonary venous pressure, no cardiomegaly, are the primary diagnostic criteria. Assessment of the pulmonary vascularity on the chest film may be difficult on supine films. Ideally, an upright film or at least a semi-erect AP radiograph should be obtained. 13 The following correlation between the chest radiograph and the pulmonary wedge pressure may be helpful: 1. The radiograph is normal when the pulmonary capillary wedge pressure (PCW) is less than 12mm. Hg. 2. When the PCW is 12-18mm. Hg, there is a redistribution of flow to the upper lobe vessels. The upper lobe vessels appear engorged and indicate mild CHF. 3. When the PCW is between 18-22mm. Hg, the peripheral vessels dilate. Interstitial edema develops in the form of Kerley lines. Kerley lines may appear as linear shadows best seen peripherally in the lungs bases (Kerley-B lines). Kerley lines may also appear as linear shadows radiating from the hilar regions (Kerley-A lines) or as reticular linear shadows throughout the lung fields (Kerley-C lines). There may also be blurring of the margins of medium-sized vessels and peribronchial cuffing or thickening. 4. Further elevation of the PCW above 22mm. Hg results in fluid in the alveoli or alveolar edema. Cardiomegaly and pleural effusions are inconsistent findings. The radiography may also lag several hours behind the PCW in the patient’s course. Other factors may alter the appearance of classic congestive failure such as pulmonary parenchymal disease and gravity. COPD commonly alters the picture of pulmonary edema. In the bedridden patient with pulmonary edema who has segmental or lobar sparing, the possibility of a recent pulmonary embolus to that area should be considered. It is often difficult to distinguish cardiogenic pulmonary edema from other causes of bilateral infiltrates such as pneumonia and ARDS. If the patient is placed in the decubitus position for a prolonged period of time, edema will increase on the dependent side and diminish on the contralateral side, whereas other infiltrates will not diminish. MONITORING APPARATUS 1. Endotracheal Tubes The proper radiographic evaluation of the endotracheal tube position requires an estimate of the position of the tube tip relative to the carina and a knowledge of the position of the head and neck at the time of the radiograph. There is considerable movement of the endotracheal tube relative to the carina with flexion and extension of the head and neck. There is descent of the tube with flexion of the neck and ascent of the tube with extension. The combined excursion of the tip of the tube may be as 14 much as 4 cm. When the head and neck are in the neutral position, the inferior border of the mandible overlies C5 to C6. In full flexion the mandible is over the upper thoracic spine and in full extension the mandible is above C4. Ideally, the tip of the endotracheal tube should be 5-7 cm. above the carina in the neutral position. One of the most common aberrant positions for the endotracheal tube is extension into the right main stem bronchus. This may result in atelectasis of the left lung with shift of the mediastinum to the left and hyperlucency of the right lung. If the endotracheal tube enters the bronchus intermedius, the right upper lobe may also collapse. 2. Tracheostomy Tubes The tub tip should be located approximately one-half to two-thirds the distance between the tracheal stoma and the carina. T3 is usually a satisfactory position. The lumen of the tracheostomy tube should be approximately two-thirds the diameter of the trachea. Pneumothorax, pneumomediastinum, and subcutaneous emphysema are frequent sequelae of tracheostomy. 3. Subclavian Vein Catheters The optimal location of the catheter tip is within the superior vena cava or at the cavo-atrial junction. It is important to look for aberrant positioning such as an extravascular location or extension into the jugular vein. Catheters may also extend into the right ventricle of extrathoracic locations. Pneumothorax is a frequent complication and if possible, an upright film is the most helpful in evaluation for the detection of pleural air and the visceral pleural line. Films in expiration may also accentuate the pneumothorax and aid in detection. 4. Swan-Ganz Catheters The tip of the catheter is ideally positioned so that it is within the right or left main pulmonary artery. Inflation of the balloon causes the catheter to float downstream into a wedge position and deflation of the balloon allows the catheter to recoil into the central pulmonary artery. Potential complications are pulmonary infarction distal to the tip of the catheter and occurs as a result of occlusion of the pulmonary artery by the catheter itself or from clot formation in or about the catheter. Other aberrant positions of the Swan-Ganz catheter may be extension into a jugular vein or out the right atrium into a hepatic vein. 15 INDICATIONS FOR THE PERFORMANCE OF CHEST RADIOGRAPHY: A. Evaluation of signs and symptoms potentially related to the respiratory, cardiovascular, and upper gastrointestinal systems, and the musculoskeletal system of the thorax. The chest radiograph may also help to evaluate thoracic disease processes, including systemic and extrathoracic diseases that secondarily involve the chest. Because the lungs and bony thorax are frequent sites of metastases, chest radiography may be useful in staging extrathoracic as well as thoracic neoplasms. B. Follow-up of known thoracic disease processes to assess improvement, resolution, or progression. C. Monitoring of patients with life-support devices and patients who have undergone cardiac or thoracic surgery or other interventional procedures. D. Compliance with government regulations that may mandate chest radiography. Examples include surveillance PA chest radiographs for active tuberculosis or occupational lung disease or exposures, or other surveillance studies required by public health law. E. Preoperative radiographic evaluation when cardiac or respiratory symptoms are present or when there is a significant potential for thoracic pathology that may influence anesthesia or the surgical result or lead to increased perioperative morbidity or mortality. INDICATIONS FOR THE PERFORMANCE OF CHEST CT: Chest CT may be a complementary examination to other imaging studies such as chest radiography (see the ACR–SPR Practice Guideline for the Performance of Chest Radiography) or a stand-alone procedure. A. Evaluation of abnormalities discovered on chest radiographs. B. Evaluation of clinically suspected thoracic pathology. C. Staging and follow-up of lung and other primary thoracic malignancies, and detection and evaluation of metastatic disease. D. Evaluation for thoracic manifestations of known extrathoracic diseases. E. Evaluation of known or suspected thoracic vascular abnormalities (congenital or acquired). F. Evaluation of known or suspected congenital thoracic anomalies. G. Evaluation and follow-up of pulmonary parenchymal and airway disease. H. Evaluation of trauma. I. Evaluation of postoperative patients and surgical complications. J. Performance of CT-guided interventional procedures. K. Evaluation of the chest wall. L. Evaluation of pleural disease. M. Treatment planning for radiation therapy. 16 17