Review for ResidentsRadiology             Robert T. Bramson, MD                     Interpretation of Chest             N....
During expiration, the airways narrow           of the peripheral airways to the resistance            ESSENTIALS         ...
hunger causes retractions and grunting                                                                                    ...
Radiology                      Figure 2. (a) Diagram shows that during normal inspiration and expiration, there is dilatio...
Radiology                      Figure 4. (a) Anteroposterior radiograph of normal chest in a 4-month-old child referred be...
Radiology                     Figure 6. (a) Anteroposterior radiograph shows hyperinflated lungs with suggestion that perib...
Radiology                      Figure 8. Respiratory syncytial virus infection in a child. (a) Anteroposterior radiograph ...
ing of the appearance of the infant chest         4. O’Brodovich H, Haddad G. Functional ba-          9. Denny F. Acute lo...
Upcoming SlideShare
Loading in...5

Cough and fever


Published on

Published in: Education, Health & Medicine
1 Like
  • Be the first to comment

No Downloads
Total Views
On Slideshare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Cough and fever

  1. 1. Review for ResidentsRadiology Robert T. Bramson, MD Interpretation of Chest N. Thorne Griscom, MD Robert H. Cleveland, MD Radiographs in Infants with Published online before print 10.1148/radiol.2361041278 Radiology 2005; 236:22–29 Cough and Fever1 1 From the Department of Radiol- An understanding of the appearance of the infant chest radiograph requires an ogy, Children’s Hospital, Boston, understanding of the anatomy and the physiologic, immunologic, and pathologic 300 Longwood Ave, Boston, MA 02115. Received July 22, 2004; revi- processes in the infant’s chest. The authors describe the features of the infant chest sion requested September 22; revi- that most influence the appearance of the chest radiograph in infants with cough sion received November 10; accepted and fever. They discuss why confusion sometimes occurs when radiology residents December 10. Address correspon- dence to R.T.B. (e-mail: robert.bramson and general radiologists familiar with adult chest radiographs first evaluate the infant chest radiograph. The radiographic appearance of acute inflammation does © RSNA, 2005 not look the same in infants as it does in older children and adults. The hallmark of inflammatory lung disease in the infant chest is air trapping on the chest radiograph. © RSNA, 2005 EDITOR’S NOTE: Please see the January 2005 From the Editor, where this new feature, Review for Residents, was announced. Radiology residents have often expressed to us their frustration and confusion when attempting to interpret chest radiographs of infants. Radiologists not trained in pediatric radiology find terms like air trapping, peribronchial thickening, bronchiolitis, lower re- spiratory tract infection, and peribronchial pneumonia confusing (1). Pediatric radiolo- gists have, in fact, conflicting definitions of these terms and varying opinions about their meaning. The authors hope to clarify the relationship between the pathologic changes within the infant chest and their radiographic appearance, explaining in pathophysiologic terms why the infant chest looks the way it does in inflammatory airways diseases. An understanding of the infant chest radiograph requires a review of how embryology, anatomy, physiology, pathology, immunology, and the physics of fluid mechanics influence its appearance. This knowledge is critical in the interpretation of the infant chest radiograph. EMBRYOLOGY AND ANATOMY We will summarize the science that explains the appearance of the infant chest, with the caveat that universal agreement on the details does not exist. All of the generations of the airways have developed by the time the fetus reaches the 16th week of gestational age. There are about 22 generations of airways, depending on how the last generation is counted and where the count is performed. Near the lung hila, there may be as few as 10 generations of airways before the gas-exchange units—the respiratory bronchioles and alveolar sacs—are reached. In the lung periphery, there may be as many as 25 generations of airways before the gas-exchange units are reached. As the child grows and becomes an adult, the airways grow in length and diameter but not in number (2– 4) (Fig 1). The alveoli, the gas-exchange units, develop after the airways. They start proliferating about the 29th week of gestational age. By the 40th week of gestation, there are approx- imately 20 million alveoli in the newborn lung, although the precise number is debated. The mature lung contains approximately 300 million alveoli; that number is reached at about 8 years of age (2). The alveoli then increase in size, and their lining gets progressively thinner as the child becomes an adult. The total alveolar surface area is 70 – 80 m2 in the adult. In the newborn infant, the total alveolar surface area is only about 3 m2. The ratio of the alveolar surface area to the body surface area is more than three times as great in the adult as in the newborn (5). Thus, the infant is at a distinct disadvantage, compared with 22
  2. 2. During expiration, the airways narrow of the peripheral airways to the resistance ESSENTIALS and the cross-sectional area decreases. of flow is considerably greater in infants This normal variation in luminal size is than in adults, even in normal circum- ● Most respiratory infections are caused accentuated in the infant because the stances (4). by viruses in infants and children support tissues around the airways are When breathing at 16 times perRadiology younger than 24 months and lead to more compliant and allow more narrow- minute, the adult has 3.75 seconds to the pathophysiologic changes of air ing during expiration. Compared with an move his or her diaphragm through the trapping. adult, the number of alveoli is relatively full course of inspiration and expiration. low in the infant, and the proportion of When breathing at 40 times per minute, ● Hyperinflation may be the only radio- the lung involved in air transport (the the infant has only 1.5 seconds for this logic clue to illness. airways) is relatively high. In the adult, diaphragm movement. The infant in- ● Bacterial pneumonia can have the 80% of the airways are bigger than 2 mm creases oxygen exchange primarily by in- same appearance in adults and in- in diameter. The smaller peripheral air- creasing the respiratory rate. When this fants. ways in adults account for less than 20% happens, the diaphragm must change di- ● The radiographic appearance reflects of the total resistance to the flow of air. In rection more frequently and either move the infant lung, the peripheral airways faster or not move as far during each the pathologic process occurring in the are considerably smaller, and the resis- excursion. During periods of respiratory respiratory system. tance to air flow owing to these small distress, these all occur. airways is 50% of the total resistance (4) The level of the diaphragm seen on (Fig 2). chest radiographs is determined by sev- eral things. At all ages, the level of the the adult and older child, in his or her diaphragm depends on how deep an in- reserve of alveolar surface area for gas PHYSIOLOGY spiration the patient has made when the exchange. The alveolar walls contain the radiograph was obtained. The adult usu- pulmonary capillaries, which form a gi- Growth is proportionately more rapid in ally takes a deep breath when requested, ant blood surface area for the exchange infancy than at any other time of post- and the diaphragm level is determined of respiratory gases (4). natal life. The metabolic requirements for by voluntary action. The infant does not The adult lung and that of the older that growth include large amounts of ox- voluntarily take a deep breath and hold it child have communications between ygen (6). However, as previously men- for a chest radiograph. The technologist the alveoli, the pores of Kohn (intraal- tioned, the adult lung has a ratio of sur- must guess and acquire the radiograph veolar pores), and the channels of Lam- face area of the pulmonary capillary bed when the infant appears to have bert (bronchoalveolar channels). These (gas-exchange area) to body surface area achieved maximum inspiration. If the in- allow collateral air drift between the that is more than three times as large as fant diaphragm moves through the en- airspaces and are far fewer in infants. that in the newborn infant (5). tire respiratory cycle in only 1.5 seconds, Their relative absence influences the The healthy newborn infant breathes or even less time when the rate reaches appearance of radiographs in infants 40 times per minute. The healthy adult 60 breaths per minute, the technologist with lower respiratory infection, as will breathes 16 times per minute. The high has little time to make a correct guess. be explained later (4). demand for oxygen in the healthy infant The diaphragm sits at a level determined The structure of the chest wall in the plus the relatively small gas-exchange by the resistance to flow of air through infant differs from that in the adult. The area per unit of body surface area taxes the airways. Figure 3 depicts lung vol- infant’s ribs and adjacent soft tissues are the respiratory system much more in the umes and diaphragm movement during more elastic and compliant. As the child infant than in the adult. This is one of respiration, first in health and then in grows, the soft tissues and ribs become the causes of the relative tachypnea of disease, when air trapping has led to an stiffer (6). Watching a baby breathe healthy infants. Infants compensate for increase in residual volume (8). makes this obvious. The infant moves his increased oxygen demand primarily by Normally, the dome of the right hemi- or her chest wall in and out more than increasing their respiratory rate (4,7). diaphragm at inspiration is projected at the adult does, particularly when in re- Resistance to the flow of air through about the level of the sixth anterior rib spiratory distress. The more marked com- the airways is higher in the infant than in on a chest radiograph. A normal lateral pliance of the soft tissues of the infant the adult. This is both because the com- chest radiograph will show a domed, thorax allows retractions of those tissues pliance of the tissues surrounding the in- rounded configuration of the diaphragm. between the ribs. The lack of stiffness in fant airways makes it easier for the air- Figure 4 shows the typical configuration the soft tissues requires more work dur- ways to narrow during normal expiration of the diaphragm on anteroposterior and ing breathing. When the infant is in re- and because of the higher percentage of lateral chest images in a healthy small spiratory distress, this increased work be- small airways in the infant lung (4). The infant. comes more obvious. The sight of a sick resistance of the flow of air through a infant struggling to breathe can be fright- cylinder, such as an airway, is described ening, and the grunting and retractions by the Poiseuille law. A quick summary IMMUNOLOGY AND graphically demonstrate the increased of this law is that the resistance to the PATHOLOGY work of breathing. In contrast, adults flow of air through the airways varies in- with pneumonia do not work particu- versely with airways radius to the fourth Growing children are exposed to many larly hard moving air in and out of their power (4). Thus, a tiny decrease in the infectious organisms and need to de- lungs unless the pneumonia is extensive. diameter of the airways leads to a marked velop immunity to them. The average During inspiration, the intrathoracic increase in resistance to the flow of air. As adult inhales more than 9000 L of air per airways increase in cross-sectional area. previously mentioned, the contribution day; the infant, much less (4). A multi- Volume 236 Number 1 Chest Radiographs in Infants with Cough and Fever 23
  3. 3. hunger causes retractions and grunting as they work to overcome this resis- tance. Infants breathing at 60 or more times per minute have less time to move theRadiology diaphragm through its inspiratory-expi- ratory cycle. They have only 1 second, sometimes less, for each breath. The dia- phragm tends to move in a narrow range because of the resistance to the flow of air through their small airways (Fig 3). The dead space in the upper airways cannot be reduced and remains constant. However, it gets more difficult to propel the dead-space air back up and out of the Figure 1. Diagram shows gas exchange that occurs in the respiratory mouth because of the increased resis- bronchiole and alveolar sac. In the lung periphery there may be as tance in the peripheral airways. As the many as 25 generations of airways before the respiratory bronchiole is reached or as few as 10 (near the hila), depending on where the count rising diaphragm pushes the air out of is performed. Inset shows how a distal bronchiole may become nar- the lungs, it must almost immediately rowed with edema and mucus during inflammation. contract to start inspiration. The inspira- tion starts before the usual volume of air has been expelled. Because of the diffi- tude of organisms enter the airways all of these lower respiratory tract infections culty of pushing all the air out during along with this inspired air. The organ- in the attempt to avoid the confusion in expiration, the lungs are at a more ex- isms that infect the respiratory tract in terminology. panded state when inspiration starts infancy are usually viral. The most severe Radiologists should be aware that the again—that is, there is an increase in re- diseases in the lower respiratory tract are nomenclature is confusing. Heated de- sidual volume, and there is air trapping caused by the parainfluenza viruses and bates may occur between physicians (Fig 3). The lungs are at a high volume the respiratory syncytial virus (9,10). who use different definitions for these even at the end of expiration. On a radio- These are also among the most common terms. We suggest that radiologists use graph, the diaphragm is projected at a organisms to infect the infant’s respira- the terms and definitions generally em- level lower than the sixth anterior rib (Fig tory tract (9 –11). Adults have some im- ployed by the referring clinicians and 6), and the diaphragm leaves are flat- munity to most of these organisms be- be alert to the problem of confusion. tened. The radiologist will notice that cause they were exposed to them as During these respiratory viral infec- there is an increase in the transverse di- children and developed an immunity. Al- tions, the airways react in several ways, ameter of the chest and a flattened dia- though adults may be infected and trans- most notably with bronchoconstriction phragm on an anteroposterior projec- mit these viruses to others, they usually and increased secretion of mucus (12). tion. On a lateral image, there is flatten- become no more than mildly ill. Infants These two factors have the effect of nar- ing of the diaphragm, and the sternum have not yet developed substantial im- rowing the cross-sectional area of the may be bowed upward and outward (Fig munity to these viruses and often get sick airways—particularly the small airways 7). Some radiologists gauge hyperaera- because of them, especially the parainflu- (12th generation airways or smaller) (Fig tion by counting posterior ribs, particu- enza and respiratory syncytial viruses. 5). These airways, which already contrib- larly if the radiograph is obtained with The terminology for lower respiratory ute 50% of the total airways resistance, the patient in an apical lordotic position. tract infections in infants is confusing. suddenly have a marked decrease in av- Those who use posterior ribs in this situ- For example the definition of bronchioli- erage radius. Since resistance is inversely ation usually believe the diaphragm is tis varies with local pediatric usage. Some proportional to the fourth power of the located at the level of the eighth poste- physicians limit the term bronchiolitis to radius, this has the effect of greatly in- rior rib during normal inspiration (8). respiratory syncytial virus infection in creasing the total resistance to air flow To diagnose air trapping, the dia- children. Affected children may have re- through the airways. phragm needs to be flattened on both tractions, tachypnea, air hunger, and ex- anteroposterior and lateral projections. If treme respiratory distress. Other children the lung volume is high on one radio- of a similar age may have the same clin- RADIOLOGIC FINDINGS graph and normal on the other, then the ical findings, but respiratory syncytial vi- high-volume projection happened to be rus cannot be cultured; some pediatri- As was mentioned earlier, the primary exposed at a moment of an unusually cians also call this bronchiolitis. Other way for the infant to increase ventila- deep breath. If the diaphragm is well physicians may call all these clinical find- tion is to increase his or her respiratory domed on the other view, then the infant ings pneumonia, but still others are un- rate. Infants in respiratory distress due is able to move air out of his or her lungs comfortable with that term because, to to viral infection often breathe 60 – 80 during expiration and there is no air trap- them, pneumonia means airspace con- times per minute. Their air hunger can ping. solidation on a chest radiograph. Some- be recognized by the use of the acces- To summarize, these sick infants times the term peribronchial pneumonia or sory respiratory muscles. The increased breathe faster and work harder to interstitial pneumonia is used to differen- work of breathing is largely caused by breathe, their airways narrow during ex- tiate this airways infection from airspace the increased resistance to the flow of piration, and the greatly increased air- pneumonia. Some individuals simply call air through the small airways. Their air ways resistance severely impedes the flow 24 Radiology July 2005 Bramson et al
  4. 4. Radiology Figure 2. (a) Diagram shows that during normal inspiration and expiration, there is dilation and collapse of the airways. This is most obvious in distal airways. Collapse in infant airways is greater than that in adult airways because cartilaginous soft tissues supporting the airways are more compliant in children. This is illustrated on (b) a lateral chest radiograph of an infant obtained near the end of normal expiration. The trachea (arrows) collapses to a much smaller diameter during normal expiration. of air. The air trapping revealed by the increase in lung volume on the chest ra- diograph is the best available indicator of inflammatory lung disease in infancy. Hyperinflation may be the only radio- logic clue to illness in these children. The alveoli are usually clear, and there is none of the airspace consolidation asso- ciated with classic bacterial pneumonia in adults. The radiologist should not become wedded to the relationship of the dia- phragm to the sixth anterior rib, but this finding does serve as a useful rule of thumb. An experienced pediatric radiol- ogist quickly recognizes hyperaeration at Figure 3. Graph depicts lung volumes at inspiration and expiration. a glance without counting ribs. A less Line on the left shows lung volume at expiration (A) and inspiration experienced observer will find the sixth (B), as well as maximum expiration (C) and inspiration (D) during anterior rib to be a helpful landmark. normal quiet respiratory cycles. The line on the right shows that when peripheral small-airways resistance is high (a, b), then residual There are often additional signs of in- volume (RV) is increased. This is the air trapping depicted on radio- flammatory disease of the small airways. graphs of infants with small-airways disease. c Maximum expira- Edema and mucus in these airways can tion, d maximum inspiration, ERV expiratory reserve volume, cause peripheral atelectasis. Small plugs IRV inspiratory reserve volume, TLC total lung capacity, TV in many small airways produce many tidal volume, VC vital capacity. (Reprinted, with permission, from small patches of atelectasis. If enough of reference 7.) these small patches accumulate in one region, a patch of atelectasis shows up on a chest radiograph (Fig 8). The abnormal cept that the interstitial lung tissues look bronchial cuffing or peribronchial thickening appearance is often difficult to define, ex- prominent. Some observers call this peri- or bronchial wall thickening. Sometimes Volume 236 Number 1 Chest Radiographs in Infants with Cough and Fever 25
  5. 5. Radiology Figure 4. (a) Anteroposterior radiograph of normal chest in a 4-month-old child referred because of a possible fractured clavicle. (b) Lateral radiograph in the same infant shows rounded configuration of the diaphragm (arrows). As the infant improves, interesting things happen. The diaphragm returns to a more normal level, but the radiograph may show increasing patches of atelecta- sis. This can confuse pediatricians and radiologists alike. Perhaps as the hyper- expansion of the lung decreases, some alveoli kept open by the air trapping now succumb and collapse, leading to an ap- pearance of increased atelectasis. In real- ity, the child is improving even though the radiograph may look mildly worse. CAVEATS The changes we have described are the most common ones in lower-airways in- flammatory disease in infancy. Most re- spiratory infections in this age group are caused by viruses and lead to the patho- physiologic changes described. Yet, just Figure 5. Diagram shows that during viral infection, airways secrete like adults, infants can also get bacterial increased amounts of mucus and become edematous, particularly in infections. In those cases, the radio- smaller peripheral airways. This narrows the airways, and that nar- graphic appearance mimics that seen on rowing is accentuated during attempts at expiration. a chest radiograph in an adult with bac- terial pneumonia. Air bronchograms, consolidation, and some volume loss in the radiologist looks at the airways end change than does thickening of the air- the consolidated segment usually do not on. If the radiologist thinks the walls ways that are identifiable on a radio- confuse radiology residents and general of these airways (usually of the third, graph. The patches of peripheral atelecta- radiologists, even when seen in infants. fourth, or fifth generation) look thicker, sis may shift when the infant coughs and Pneumonia looks the same in adults, he or she will use the term peribronchial dislodges small mucus plugs. Therefore, and, when bacterial, it can look that way thickening or bronchial wall thickening. In the radiographic appearance may change in infants too. Infants with bacterial reality, thickening of the smaller air- from image to image. Hyperinflation, how- pneumonia can have pleural effusions ways (12th generation or higher) has a ever, remains the major clue to inflamma- and adenopathy. Children are not im- far more deleterious effect on gas ex- tory small-airways disease (12). mune to the types of pulmonary infec- 26 Radiology July 2005 Bramson et al
  6. 6. Radiology Figure 6. (a) Anteroposterior radiograph shows hyperinflated lungs with suggestion that peribronchial markings are too prominent. (b) Lateral radiograph shows flat slope to the diaphragm, with none of the rounded configuration seen in Figure 4b. The diaphragm now has a straight-line slope rather than a rounded configuration. Figure 7. (a) Anteroposterior radiograph of infant chest shows hyperinflated appearance characteristic of infant inflamma- tory airways disease. Hemidiaphragm domes are projected at level of the seventh anterior rib or lower. (b) Lateral radiograph of hyperinflated chest shows diaphragm has a straight (not domed) slope. tions that older children and adults con- sometimes produce an unusual and dis- are fewer pores of Kohn and channels of tract. Nevertheless, viruses are the most concerting appearance because of the an- Lambert. Therefore, exudate that accu- common cause of respiratory infections atomic features mentioned earlier. The mulates in the alveoli does not spread to in infants (10). infant does not have a well-developed adjacent alveoli as easily as in the adult. Bacterial pneumonia in infancy can system of collateral ventilation—there The limits of the inflammatory process Volume 236 Number 1 Chest Radiographs in Infants with Cough and Fever 27
  7. 7. Radiology Figure 8. Respiratory syncytial virus infection in a child. (a) Anteroposterior radiograph shows prominent peribronchial markings. (b) Patches of atelectasis (arrow) are best seen on lateral projection of the hyperinflated lungs. Scattered patches of atelectasis tend to follow peribronchial and perivascular structures in a child with respiratory syncytial virus infection. cause a round pneumonia can look like a neoplasm (13). Several children have been referred to us with the suspicion of a primary or metastatic neoplasm, but they really had pneumonia with an un- usual spherical appearance (Fig 9). Other disease processes can produce air trapping and hyperaeration of the lungs. Increased fluid in the interstitial spaces can compress the small airways and cause an increase in small-airways resistance. Enlarged heart chambers and pulmonary vessels can also compress airways. There- fore, severe cardiac disease and increased fluid load can lead to radiographs that show air trapping. Older infants can and do aspirate foreign bodies into their air- ways; this may cause focal air trapping or atelectasis. Reactive airways disease, which does occur in infants, can cause air trapping at any age. Certain chronic lung diseases such as cystic fibrosis and bron- Figure 9. Anteroposterior chest radiograph displays round chopulmonary dysplasia demonstrate pneumonia (arrow). Child had a fever of 104°F (40°C), abdom- air trapping on radiographs. Tachypnea inal pain, and a cough. from a variety of other causes, such as acidosis, fever, and sometimes even fear, will produce the appearance of air trap- are difficult to define in adults unless takes the appearance of a spherical con- ping secondary to the mechanism of they border on a pleural surface. In in- solidation—a “round pneumonia”. The rapid breathing (4). fants and younger children, however, the inflammatory cells are confined under a Nevertheless, most infants who acutely exudate tends to be trapped in the alve- mild degree of pressure, and these infants develop respiratory distress have a viral oli, unable to spread through the pores of often have a high fever; 104°F or 105°F illness. The appearance of the radiograph Kohn. Sometimes, because of the lack of (40°C or 41°C) is typical. The radio- reflects the pathologic process occurring collateral air drift openings, the exudate graphic appearance can be alarming be- in the respiratory system. An understand- 28 Radiology July 2005 Bramson et al
  8. 8. ing of the appearance of the infant chest 4. O’Brodovich H, Haddad G. Functional ba- 9. Denny F. Acute lower respiratory tract in- radiograph requires an understanding of sis of respiratory pathology and disease. In: fection: general considerations. In: Tauss- Chernick V, Boat T, eds. Kendig’s disorders ing L, Landau L, eds. Pediatric respiratory the underlying pathologic process. Hyper- of the respiratory tract in children. 6th ed. medicine. St Louis, Mo: Mosby, 1999. aeration of the lungs is often the earliest, Philadelphia, Pa: Saunders, 1998; 27–73. 10. Dubois D, Ray C. Viral infections of the and sometimes the only, radiographic 5. Dunnill MS. Postnatal growth of the lung. lower respiratory tract. In: Taussing L, sign that the infant has a viral infection Thorax 1962; 17:329 –333. Landau L, eds. Pediatric respiratory medi-Radiology 6. Mortola J. Comparative aspects of neona- cine. St Louis, Mo: Mosby, 1999. involving the lower airways. tal respiratory mechanisms. In: Haddad G, 11. Gern J. Virus-induced inflammation in air- Abman S, Chernick V, eds. Chernick-Mel- ways. In: Haddad G, Abman S, Chernick V, lin: basic mechanisms of pediatric respira- eds. Chernick-Mellins: basic mechanisms References tory disease. 2nd ed. Hamilton, Ontario, of pediatric respiratory disease. 2nd ed. 1. Coblentz C, Babcook C, Alton D, Riley B, Canada: Decker, 2002; 171–178. Hamilton, Ontario, Canada: Decker, 2002; Norman G. Observer variation in detecting 7. Lawson E. Respiratory control after birth. 518 –527. the radiologic features associated with In: Chernick V, Mellin R, eds. Basic mech- 12. Swischuk LE, Hayden CK Jr. Viral vs. bac- bronchiolitis. Invest Radiol 1991; 26:115– anisms of pediatric respiratory disease: cel- terial pneumonia infection in children (is 118. lular and integrative. Philadelphia, Pa: roentgenographic differentiation possi- 2. Reid L. Lung growth in health and disease. Decker, 1991; 288 –302. ble?). Pediatr Radiol 1986; 16:278 –284. Br J Dis Chest 1984; 78:113–134. 8. Griscom NT, Wohl M, Kirkpatrick J. Lower 13. Rose R, Ward B. Spherical pneumonias in 3. Hislop A, Reid L. Lung development in rela- respiratory infections: how infants differ children simulating pulmonary and medi- tion to gas exchange capacity. Bull Physio- from adults. Radiol Clin North Am 1978; astinal masses. Radiology 1973; 106:179 – pathol Respir (Nancy) 1973; 9:1317–1343. 16:367–387. 182. Volume 236 Number 1 Chest Radiographs in Infants with Cough and Fever 29