CHAPTER THREE Chest The chest radiograph is one of the most com- monly obtained examinations in pediatric imag- ing. It is also the examination most likely to be encountered by radiology residents, pediatric residents, general radiologists, and pediatricians. Therefore, topics such as chest imaging in neo- nates and the evaluation of suspected pneumo- nia are discussed in detail. NEONATAL CHEST Causes of respiratory distress in newborn infants can be divided into those that are secondary to diffuse pulmonary disease (medical causes) and those that are secondary to a space-occupying mass compressing the pulmonary parenchyma (surgical causes). Diffuse Pulmonary Disease in the Newborn Diffuse pulmonary disease causes respiratory distress much more commonly than surgical dis- eases, particularly in premature infants, who make up the majority of cases of respiratory dis- tress in the newborn. A simple way to evaluate these patients and try to offer a limited differen- tial diagnosis is to evaluate the lung volumes and to characterize the pulmonary opacities. Lung volumes can be categorized as high, normal, or low. Normally, the apex of the dome of the diaphragm is expected to be at the level of approximately the tenth posterior rib. Lung opa- city, if present, can be characterized as streaky, perihilar (central) densities that have a linear quality or as diffuse, granular opacities that have an almost sandlike character. Classically, cases fall into one of the following two cate- gories: (1) cases with high lung volumes and streaky perihilar densities and (2) cases with low lung volumes and granular opacities (Table 3-1). This is more of a guideline, rather than a rule, because many neonates with diffuse pulmonary disease have normal lung volumes. The differential diagnosis for cases with high lung volumes and streaky perihilar densities includes meconium aspiration, transient tachyp- nea of the newborn, and neonatal pneumonia. Most of the neonates in this group are term. The differential for cases with low lung volumes and granular opacities includes surfactant deficiency and b-hemolytic streptococcal pneumonia. Most of these neonates are premature. Meconium Aspiration Syndrome Meconium aspiration syndrome results from intrapartum or intrauterine aspiration of meconi- um. It usually occurs secondary to stress, such as hypoxia, and more often occurs in term or post- mature neonates. The aspirated meconium causes both obstruction of small airways sec- ondary to its tenacious nature and also chemical pneumonitis. The degree of respiratory failure can be severe. Radiographic findings include hyperinflation (high lung volumes), which may be asymmetric and patchy, and asymmetric lung densities that tend to have a ropy appear- ance and a perihilar distribution (Fig. 3-1). Commonly there are areas of hyperinflation alternating with areas of atelectasis. Pleural effu- sions can be present. Because of the small- airway obstruction by the meconium, air-block complications are common, with pneumothorax occurring in 20% to 40% of cases. Meconium aspiration syndrome is relatively common; 25,000 to 30,000 cases occur in the United States annually. Transient Tachypnea of the Newborn Transient tachypnea of the newborn (TTN) is also referred to by a variety of other names, including wet lung disease and transient respira- tory distress. It occurs secondary to delayed clearance of fetal lung fluid. Physiologically, the clearing of fetal lung fluid is facilitated by the ‘‘thoracic squeeze’’ during vaginal deliveries; therefore, most cases of TTN are related to 26 cesarean section in which the thoracic squeeze is bypassed. Other causes include maternal dia- betes and maternal sedation. The hallmark of TTN is a benign course. Respiratory distress develops by 6 hours of age, peaks at 1 day of age, and is resolved by 2 to 3 days. There is a spectrum of radiographic findings similar to those seen with mild to severe pulmonary edema. There is a combination of airspace opaci- fication, coarse interstitial markings, prominent and indistinct pulmonary vasculature, fluid in the fissures, pleural effusion, and cardiomegaly (Fig. 3-2). Lung volumes are normal to increased. Neonatal Pneumonia Neonatal pneumonia can be caused by a large number of infectious agents that can be acquired intrauterine, during birth, or soon after birth. With the exception of b-hemolytic streptococcal pneumonia, which will be discussed sep- arately, the radiographic appearance of neonatal pneumonia is that of patchy, asymmetric perihi- lar densities and hyperinflation (Fig. 3-3). Pleural effusions may be present (Fig. 3-4). Such cases of neonatal pneumonia may have a similar radiographic appearance to and be indistin- guishable from meconium aspiration syndrome when using imaging alone. Surfactant-Deficient Disease Surfactant-deficient disease (SDD; also referred to as respiratory distress syndrome or hyaline membrane disease) is a common disorder, with approximately 40,000 new cases annually in the United States. It is primarily a disease of prema- ture infants, affecting up to 50% of them, and it is the most common cause of death in live new- borns. SDD is related to the inability of prema- ture type II pneumocytes to produce surfactant. Normally, surfactant coats the alveolar surfaces and decreases surface tension, allowing for the alveoli to remain open. As a result of the lack of surfactant, there is alveolar collapse, resulting in noncompliant lungs. The radiographic findings reflect these pathologic changes (Fig. 3-5A, B). TABLE 3-1. Differential Diagnosis of Diffuse Pulmonary Disease in the Newborn High lung volumes, streaky perihilar densities Low lung volumes, granular opacities Meconium aspiration syndrome Transient tachypnea of the newborn Neonatal pneumonia Surfactant deficiency b-hemolytic streptococcal pneumonia FIGURE 3-1. Meconium aspiration syndrome. Newborn chest radiograph shows normal to large lung volumes, increased peri- hilar markings, and bilateral, coarse, ropy markings. Note right pleural effusion (arrow). FIGURE 3-2. Transient tachypnea of the newborn. Newborn chest radiograph shows normal lung volumes, cardiomegaly, indistinct pulmonary vascularity, and fluid in the minor fissure (arrow). Within 24 hours the patient was asymptomatic. Chest • 27 Lung volumes are low. There are bilateral gran- ular opacities that represent collapsed alveoli interspersed with open alveoli. Because the larger bronchi do not collapse, there are prom- inent air bronchograms. When the process is severe enough and the majority of alveoli are collapsed, there may be coalescence of the gran- ular opacities, resulting in diffuse lung opacity. FIGURE 3-3. Neonatal pneumonia. Newborn chest radiograph shows large lung volumes and coarse, bilateral perihilar markings. FIGURE 3-4. Neonatal pneumonia. Newborn chest radiograph shows large lung volumes and coarse, bilateral perihilar mark- ings. Note right pleural effusion (arrow). Also note umbilical venous catheter with tip into right atrium. Tip should be at the junction of the right atrium and inferior vena cava. A B FIGURE 3-5. Surfactant-deficient disease responding to surfactant therapy. A, Radiograph shortly after birth shows low lung volumes, confluent densities, and prominent air bronchograms. Note the umbilical venous catheter (arrow) with tip in intrahe- patic intravenous catheter. B, Radiograph obtained immediately following surfactant administration shows increased lung volumes and decreased lung opacities. The umbilical venous catheter was removed in the interim. Note the umbilical venous catheter (arrow) in ‘‘low’’-type position, with tip at L4. 28 • Pediatric Imaging: The Fundamentals A normal film at 6 hours of age excludes the presence of SDD. Surfactant Replacement Therapy One of the therapies for SDD is surfactant administration. Surfactant can be administered via nebulized or aerosol forms. It is administered into the trachea via a catheter or an adapted endotracheal tube. The administration of surfac- tant in neonates with SDD has been shown to be associated with decreased oxygen and ventilator setting requirements, decreased air-block com- plications, decreased incidence of intracranial hemorrhage and bronchopulmonary dysplasia, and decreased death rate. However, there is an associated increased risk for development of patent ductus arteriosus and pulmonary hemor- rhage, and there can be an acute desaturation episode in response to surfactant administration. Surfactant administration can be given on a rescue basis when premature neonates develop respiratory distress or can be given prophylacti- cally in premature infants who are at risk. Prophylactic administration is commonly given immediately after birth and is becoming a more common practice. In response to surfactant administration, radiography may demonstrate complete, central, or asymmetric clearing of the findings of SDD (see Fig. 3-5). There is usu- ally an increase in lung volumes. Neonates without radiographic findings of a response to surfactant have poorer prognoses than those who have radiographic evidence of a response. A pattern of alternating distended and collapsed acini may create a radiographic pattern of bub- blelike lucencies that can mimic pulmonary interstitial emphysema. Knowledge of when surfactant has been administered is helpful in rendering accurate interpretation of chest radiographs taken in the neonatal intensive care unit (NICU). b-Hemolytic Streptococcal Pneumonia b-hemolytic (group B) streptococcal pneumonia is the most common type of pneumonia in neo- nates. The infection is acquired during birth, and at least 25% of women in labor are colonized by the organism. Premature infants are more com- monly infected than are term infants. In contrast to the other types of neonatal pneumonias, the radiographic findings include bilateral granular opacities and low lung volumes (Fig. 3-6), the identical findings in surfactant-deficient disease. The presence of pleural fluid is a helpful differ- entiating factor because it is very uncommon in surfactant deficiency but has been reported in between 25% and 67% of cases of b-hemolytic streptococcal pneumonia. Persistent Pulmonary Hypertension in the Neonate Persistent pulmonary hypertension in the neo- nate, also referred to as persistent fetal circula- tion, is a term often used in the NICU and is addressed here because it can be a source of confusion. The high pulmonary vascular resis- tance that is normally present in the fetus typi- cally decreases during the newborn period. When this fails to happen, the pulmonary pres- sures remain abnormally high, and the condition is referred to as persistent pulmonary hyperten- sion. It is a physiologic finding rather than a spe- cific disease. It can be a primary phenomenon or it can occur secondary to causes of hypoxia, such as meconium aspiration syndrome, neona- tal pneumonia, or pulmonary hypoplasia associ- ated with congenital diaphragmatic hernia. These patients are quite ill. The radiographic patterns are variable and are more often FIGURE. 3-6. b-Hemolytic streptococcal pneumonia. Radiograph shows low lung volumes and diffuse granular opacities, similar in appearance to cases of surfactant deficiency. Chest • 29 reflective of the underlying cause of hypoxia than the presence of persistent pulmonary hypertension. Neonatal Intensive Care Unit Support Apparatus One of the primary roles of chest radiography in the NICU is to monitor support apparatus. They include endotracheal tubes, enteric tubes, central venous lines, umbilical arterial and venous cathe- ters, and extracorporeal membrane oxygenation (ECMO) catheters. The radiographic evaluation of many of these tubes is the same as that seen in adults and is not discussed here. When evalu- ating the positions of endotracheal tubes in pre- mature neonates, it is important to consider that the length of the entire tracheamay be only about 1 cm. Keeping the endotracheal tube in the exact center of such a small trachea is an impossible task for caregivers, and phone calls and reports suggesting that the tube needs to be moved 2mm proximally may be more annoying than helpful. Direct phone communication may be more appropriately reserved for times when the tube is in a main bronchus or above the thoracic inlet. There is an increased propensity to use esopha- geal intubation in neonates compared to its use in adults. Although it would seem that esophageal intubation would be incredibly obvious clini- cally, this is not always the case. I have seen cases in which a child has in retrospect been dis- covered to have been esophageally intubated for more than 24 hours. Therefore, the radiologist may be the first to recognize esophageal intuba- tion. Obviously, when the course of the endotra- cheal tube does not overlie the path of the trachea, the use of esophageal intubation is fairly obvious. Other findings of esophageal intubation include a combination of low lung volumes, gas within the esophagus, and gaseous distention of the bowel (Fig. 3-7). Umbilical Arterial and Venous Catheters Umbilical arterial and venous catheters are com- monly used in the NICU. Umbilical arterial catheters pass from the umbilicus inferiorly into the pelvis via the umbilical artery to the iliac artery. The catheters then turn cephalad within the aorta (see Fig. 3-5). These catheters can be associated with thrombosis of the aorta and its branches. Therefore, it is important to avoid positioning the catheter with the tip at the level of the branches of the aorta (celiac, superior mesenteric, and renal arteries). There are two acceptable umbilical arterial catheter positions: high lines have their tips at the level of the descending thoracic aorta (T8-T10; see Fig. 3-9); low lines have their tips below the level of L3 (see Fig. 3-5). The catheter tip should not be positioned between T10 and L3 because of the risk for major arterial thrombosis. There is no clear consensus as to whether a high or a low umbilical artery catheter line is better, and both positions are still currently used. The pathway of the umbilical venous cath- eter is umbilical vein to left portal vein to ductus venosus to hepatic vein to inferior vena cava (Fig. 3-8). In contrast to umbilical arterial cathe- ters, the course is in the superior direction from the level of the umbilicus. The ideal position of an umbilical venous catheter is with its tip at the junction of the right atrium and the inferior vena cava at the level of the hemidiaphragm FIGURE 3-7. Esophageal intubation in a 6-day-old girl. Chest radiograph obtained after reintubation shows the endotracheal tube overlying the expected location of the midtrachea. However, there are low lung volumes, gas within the esophagus (arrows), and multiple air-filled and distended bowel loops. 30 • Pediatric Imaging: The Fundamentals (see Figs. 3-4, 3-5). The umbilical venous cathe- ter may occasionally deflect into the portal venous system rather than passing into the ductus venosus. Complications of such position- ing can include hepatic hematoma or abscess. Peripherally Inserted Central Catheters in Children One of the more common lines now seen in children, as in adults, is peripherally inserted central catheters (PICCs). In contrast to adults, in whom some of the PICCs can be as large as 6F, the PICC lines used in children, particularly infants, are often small in caliber (2F or 3F) so that they can be placed into their very small peripheral veins. These small caliber PICCs can be very difficult to see on chest radiography, so some of them must be filled with contrast to be accurately visualized. The tip of the PICC line that enters the child from the upper extremity or scalp should be positioned with the tip in the midlevel of the superior vena cava (see Fig. 3-27). It is essential that PICC lines not be left in place with the tip well into the right atrium. Particularly with the small-caliber lines, the atrium can be lacerated, leading to pericar- dial tamponade, free hemorrhage, or death. Many such cases have been reported nationally. Also, the PICC should not be too proximal in the superior vena cava because the distal portion of the line can flip from the superior vena cava into the contralateral brachiocephalic or jugular vein. At Cincinnati Children’s Hospital Medical Center, the PICC lines are inserted in a dedicated inter- ventional radiology suite by a team of nurses, with supervision by pediatric interventional radi- ologists. Ultrasound is often used to guide vein cannulation and certified Child Life Specialists coach most kids through the procedure without having to sedate them. Fluoroscopy is utilized at the end of the procedure to adjust and docu- ment tip position in the mid-superior vena cava. EXTRACORPOREAL MEMBRANE OXYGENATION ECMO is a last-resort therapy usually reserved for respiratory failure that has not responded to other treatments. ECMO is essentially a pro- longed form of circulatory bypass of the lungs and is used only in patients who have reversible disease and a chance for survival. The majority of neonates who are treated with ECMO have respiratory failure as a result of meconium aspiration, persistent pulmonary hypertension (resulting from a variety of causes), severe con- genital heart disease, or congenital diaphrag- matic hernia. ECMO seems to be used less commonly now than it was in the 1990s. There are two types of ECMO: arteriovenous and venovenous. In ateriovenous ECMO, the right common carotid artery and internal jugular veins are sacrificed. The arterial catheter is placed via the carotid and positioned with its tip overlying the aortic arch. The venous cathe- ter is positioned with its tip over the right atrium (Fig. 3-9). One of the main roles of a chest radio- graph of children on ECMO is to detect any potential migration of the catheters. Careful comparison with previous studies to make sure that the catheters are not coming out or moving too far in is critical. These patients have many bandages and other items covering the external portions of the catheters, so migration may be hard to detect on physical examination. Note that there are various radiographic appearances of the ECMO catheters. Some catheters end where the radiopaque portion of the tube ends, and others have a radiolucent portion with a small metallic marker at the tip (see Fig. 3-9). It is common to see white-out of the lungs soon after a patient is placed on ECMO as a result of decreased ventilator settings and DV LPV RPV UV FIGURE 3-8. Anatomy of the course of the umbilical vein (UV) catheter as demonstrated by contrast injection of umbilical cath- eter performed because of inability to advance UV catheter. Note course of umbilical vein to portal vein to ductus venosus (DV; arrow). LPV, left portal vein; RPV, right portal vein. Chest • 31 third-space shifting of fluid (see Fig. 3-9). Patients on ECMO are anticoagulated and are therefore at risk for hemorrhage. Types of Ventilation: High-Frequency Oscillator vs. Conventional Ventilation High-frequency oscillators are commonly used to treat neonates in the NICU. In contrast to con- ventional ventilation, high-frequency oscillators use supraphysiologic rates of ventilation with very low tidal volumes. Conventional ventilation has been likened to delivering a cupful of air approximately 20 times a minute. In contrast, high-frequency oscillation is like delivering a thimbleful of air approximately 1000 times per minute. The air is vibrated in and out of the lung. The mechanism of oscillators is poorly under- stood. In conventional ventilation, the dia- phragm moves up and down, whereas during high-frequency ventilation the diaphragm stays parked at a certain anatomic level. This level can be adjusted by changing the mean airway pres- sure of the oscillator. Caregivers usually like to maintain the diaphragm at approximately the level of the 10th posterior ribs. In general, the radiographic appearance of neonatal pulmonary diseases is not affected by whether the patient is being ventilated by conventional or high- frequency ventilation. Complications in the Neonatal Intensive Care Unit As in adult intensive care units, major complica- tions detected by chest radiographs include those related to air-block complications, lobar collapse, or acute diffuse pulmonary consolida- tion. Another type of complication seen in neo- nates is the development of bronchopulmonary dysplasia. Imaging findings of lobar collapse and air-block complications such as pneumothorax, pneumomediastinum, and pneumopericardium are similar in neonates and in adults. One type of air-block complication that is unique to neo- nates is pulmonary interstitial emphysema. Pulmonary Interstitial Emphysema In patients with severe surfactant deficiency, ventilatory support can result in marked increases in alveolar pressure, leading to perfo- ration of alveoli. The air that escapes into the adjacent interstitium and lymphatics is referred to as pulmonary interstitial emphysema (PIE). PIE appears on radiographs as bubblelike or linear lucencies and can be focal or diffuse (Fig. 3-10). The involved lung is usually non- compliant and is seen to have a static volume on multiple consecutive films. The finding is typ- ically transient. The importance of detecting PIE is that it serves as a warning sign for other impending air-block complications such as pneumothorax, and its presence can influence caregivers in decisions such as switching from conventional to high-frequency ventilation. It can be difficult to differentiate diffuse PIE from the bubblelike lucencies that are associated with developing bronchopulmonary dysplasia. When encountering this scenario, the patient’s age can help to determine which is more likely. Most cases of PIE occur in the first week VC AC FIGURE 3-9. ECMO catheter placement for meconium aspira- tion syndrome (same child as in Fig. 3-1). Note venous ECMO catheter (VC) has a radiopaque proximal portion and a lucent distal portion. The tip of the venous catheter is marked by a small radiopaque metallic marker (arrow) and is actually in the right atrium. Note the arterial ECMO catheter (AC) with tip in region of aortic arch. Also, note ‘‘high’’-type umbilical arterial catheter with tip overlying descending aorta at the level of T8. 32 • Pediatric Imaging: The Fundamentals of life, a time at which bronchopulmonary dys- plasia is very unlikely. In patients older than 2 weeks, bronchopulmonary dysplasia is more likely. Also, in patients who have undergone a series of daily films, PIE may be noted to occur abruptly, whereas bronchopulmonary dysplasia tends to occur gradually. As previously men- tioned, SDD partially treated by surfactant replacement can cause a pattern of lucencies that may mimic PIE as well. Rarely, PIE can persist and develop into an expansive, multicystic mass. The air cysts can become large enough to cause mediastinal shift and compromise pulmonary function. Often, the diagnosis is indicated by sequential radiography showing evolution of the cystic mass from original findings typical of PIE. In unclear cases, CT demonstrates that the air cysts are in the interstitial space by showing the bronchovascular bundles being positioned within the center of the air cysts. The broncho- vascular bundles appear as linear or nodular densities in the center of the cysts. Causes of Acute Diffuse Pulmonary Consolidation Acute diffuse pulmonary consolidation is non- specific in neonates, as it is in adults, and can represent blood, pus, or water. In the neonate, the specific considerations include edema, which may be secondary to the development of patent ductus arteriosus (Fig. 3-11); pulmo- nary hemorrhage, to which surfactant therapy predisposes; worsening surfactant deficiency (during the first several days of life but not later); or developing neonatal pneumonia (Table 3-2). Diffuse microatelectasis is another possibility because neonates have the propen- sity to artifactually demonstrate diffuse lung opacity on low lung volume films (expiratory technique; Fig. 3-12A. B); this should not be mis- taken for another cause of consolidation. Such radiographs showing low lung volumes offer little information concerning the pulmonary status of the patient and should be repeated when clinically indicated. RUL FIGURE 3-10. Pulmonary interstitial emphysema in a premature infant with congenital heart disease. Chest radiograph shows asymmetric bubblelike lucencies within the left upper lobe con- sistent with PIE. Note left pneumothorax (arrow) and right upper lobe collapse (RUL). A B FIGURE 3-11. Patent ductus arteriosus (PDA) leading to conges- tive heart failure in a 1-week-old premature neonate. A, Prior to development of PDA, radiograph shows normal-sized heart and clear lungs; B, After development of PDA, radiograph shows cardiac enlargement and bilateral lung consolidation. Chest • 33 Bronchopulmonary Dysplasia Bronchopulmonary dysplasia (BPD) is also referred to as chronic lung disease of prematur- ity. It is a common complication seen in prema- ture infants and is associated with significant morbidity rates. It is uncommon in children born at greater than 32 weeks of gestational age, but it occurs in more than 50% of premature infants born at less than 1000 g. BPD is the most common chronic lung disease of infancy. BPD is related to injury to the lungs that is thought to result from some combination of mechanical ventilation and oxygen toxicity. Although four discrete and orderly stages of the development of BPD were originally described, they are not seen commonly and are probably not important to know. BPD typi- cally occurs in a premature infant who requires prolonged ventilator support. At approximately the end of the second week of life, persistent hazy density appears throughout the lungs. Over the next weeks to months, a combination of coarse lung markings, bubblelike lucencies, and asymmetric aeration can develop (Fig. 3-13). Eventually, focal lucencies, coarse reticu- lar densities, and bandlike opacities develop. In childhood survivors of BPD, many of these radiographic findings decrease in prominence over the years and only hyperaeration may per- sist. The radiographic findings may completely resolve. Clinically, many children with severe BPD during infancy may eventually improve to normal pulmonary function or may only have minor persistent problems such as exer- cise intolerance, predisposition to infection, or asthma. Wilson-Mikity syndrome is a confusing and controversial term. It refers to the development of BPD in the absence of mechanical ventilation. Some people debate whether this disease exists, whereas others think it is a variant of BPD. Certainly, there are cases in which BPD findings develop with minimal ventilator support or develop earlier than is typically expected. Focal Pulmonary Lesions in the Newborn In contrast to diffuse pulmonary disease in new- borns, focal masses can present with respiratory distress due to compression of otherwise normal lung. Most of these focal masses are related to congenital lung lesions. Congenital lung lesions may appear solid, as air-filled cysts, or mixed in appearance. The differential for a focal lung lesion can be separated on the basis of whether the lesion is lucent or solid appearing on chest radiography (Table 3-3). The most likely TABLE 3-2. Causes of Acute Diffuse Pulmonary Consolidation in Neonates Edema: patent ductus arteriosus Hemorrhage Diffuse microatelectasis: artifact Worsening surfactant deficiency (only during first days of life) Pneumonia B A FIGURE 3-12. Expiratory chest radiograph mimicking heart fail- ure in infant. A, Initial radiograph shows prominent size of cardiothymic silhouette, indistinctness of pulmonary vascularity, and low lung volumes. B, Repeat radiograph obtained immedi- ately after A shows clear lungs and normal heart size. 34 • Pediatric Imaging: The Fundamentals considerations for a lucent chest lesion in a new- born are congenital lobar emphysema, congen- ital cystic adenomatoid malformation, persistent pulmonary interstitial emphysema, and congen- ital diaphragmatic hernia. CT may be helpful in differentiating among these lesions by demonstrating whether the abnormal lucency is related to air in distended alveoli, in the interstitium, or in abnormal cystic structures. Lesions that typically appear solid during the neonatal period include sequestration and bron- chogenic cyst. Many of these lesions can present in children beyond the neonatal period, and those aspects of these entities are also dis- cussed here. The following sections are divided into spe- cific congenital lesions. However, it has been increasingly recognized that there can be ‘‘mixed’’ lesions, which show characteristics of more than one type of lesions (see Fig. 3-16). The most common mixed lesions are those that show characteristics of both congenital cystic adenomatoid malformation and sequestration. It is also worth mentioning that there has been a change in the way these lesions present that is related to the increased use of prenatal ultrasound and magnetic resonance (MR) imag- ing. Historically, congenital lung lesions were identified only when the infant became symp- tomatic. Many, if not most, of the congenital lung lesions we currently see are picked up and fol- lowed through fetal life, with additional post- natal imaging obtained shortly after birth. A significant number of these children are asymp- tomatic. This has raised issues related to when and whether to perform surgical treatment in infants with asymptomatic lesions. Congenital Lobar Emphysema Congenital lobar emphysema is related to over- expansion of alveoli, but the mechanism is debated. Some reports suggest a ball-valve type of anomaly in the bronchus leading to the affected lung, which causes progressive air trap- ping. Most cases present with respiratory distress during the neonatal period; 50% present within the first month, and 75% present within the first 6 months of life. There can be associated A B C FIGURE 3-13. Bronchopulmonary dysplasia in a premature neo- natal girl. A, Chest radiograph at 14 days of life shows persistent bilateral lung opacities. B, Chest radiograph at 20 days of life shows coarsening of the lung markings. C, Chest radiograph at 28 days of life shows increased coarse lung markings and devel- opment of diffuse bubblelike lucencies. TABLE 3-3. Focal Lung Lesions in Neonates on Radiography Lucent Lesions Solid Lesions Congenital lobar emphysema Congenital cystic adenomatoid malformation Persistent pulmonary interstitial emphysema Congenital diaphragmatic hernia Sequestration Bronchogenic cyst Congenital cystic adenomatoid malformation Chest • 35 anomalies, usually cardiac, but they occur in the minority of patients with congenital lobar emphysema. There is a lobar predilection; the most common site is the left upper lobe (43%), followed by the right middle lobe (35%) and right lower lobe (21%), with less than 1% in each of the other lobes. On chest radiography, a hyperlucent, hyperexpanded lobe is seen (Fig. 3-14A, B). On initial radiographs, the lesion may appear to be a soft tissue density because of retained fetal lung fluid. This density resolves and is replaced by progressive hyperlu- cency. On CT, the air is in the alveoli, so the interstitial septa and bronchovascular bundles are at the periphery (not the center) of the lucency (see Fig. 3-14). The air spaces are larger than those in the adjacent normal lung, and the pulmonary vessels appear attenuated. The treatment is lobectomy. Congenital Cystic Adenomatoid Malformation Congenital cystic adenomatoid malformation (CCAM) is a congenital adenomatoid prolifera- tion that replaces normal alveoli. The majority are detected prenatally or are present with respi- ratory distress at birth. Most involve only one lobe and, in contrast to congenital lobar emphy- sema, there is no lobar predilection. CCAMs are divided into three types on the basis of how large the cysts appear at imaging or pathology. Type 1 lesions (50%) have one or more large (2 to 10 cm) cysts. Type 2 lesions (40%) have numerous small cysts of uniform size. Type 3 lesions (10%) appear solid on gross inspection and imaging but have microscopic cysts. There are some who are now advocating the nomen- clature congenital pulmonary airway malforma- tion and a new classification with five subtypes. Who are these people and don’t they have any- thing better to do? The classification system has no clinical rel- evance except that it helps us remember that CCAM can have multiple appearances when imaged. The imaging appearance reflects the type. CCAMs communicate with the bronchial tree at birth and therefore fill with air within the first hours to days of life. On radiography and CT, a completely cystic, mixed cystic and solid, or completely solid mass is seen depend- ing on the number and size of cysts and whether those cysts contain air or fluid (Figs. 3-15A-C, 3-16A-C). The management of symptomatic CCAM is surgical resection. The management of asymptomatic CCAM is currently somewhat controversial. However, most caregivers advo- cate elective resection because these lesions are at increased risk for infection and, rarely, may develop malignancy. A scenario encountered with increasing fre- quency is a prenatally diagnosed lung mass that becomes less prominent on serial prenatal ultra- sounds or MR examinations and demonstrates only subtle findings or is not detected on a chest radiograph obtained soon after birth. B A FIGURE 3-14. Congenital lobar emphysema. A, Radiograph obtained at 1 day of age shows diffuse lucency and enlargement of left upper lobe (arrows). B, CT scan shows hyperlucent and enlarged left upper lobe with asymmetric attenuation of vascular structures and increased space between interstitial septa. 36 • Pediatric Imaging: The Fundamentals Almost all such lesions are type 2 CCAMs and demonstrate abnormalities on CT, even in light of a normal chest radiograph. Many CCAMs identified prenatally are fol- lowed with MR imaging (see Fig. 3-15), and much has been learned about the nature of these lesions. CCAMs tend to increase in size until approximately 25 weeks of gestation. The mass of the CCAMs then tends to regress over time, sometimes dramatically. Compression of the contralateral lung by a large mass and development of fetal hydrops are associated with high mortality rates. Fetal intervention is typically reserved for cases with hydrops; management options include dominant cyst aspiration and fetal surgery with resection of the lesion. Recently, trials using maternal steroids have shown promise in shrinking the CCAM volumes and avoiding other interventions. Congenital Diaphragmatic Hernia Congenital diaphragmatic hernias (CDHs) are usually secondary to posterior defects in the diaphragm (Bochdalek hernia) and are more common on the left side by a ratio of 5 to 1. Most infants with CDHs present at birth with severe respiratory distress. The hernia may con- tain stomach, small bowel, colon, or liver. The radiographic appearance depends on the hernia contents and on whether there is air within the herniated viscera. On initial radio- graphs, prior to the introduction of air into the viscera, the appearance may be radiopaque. C B R A FIGURE 3-15. Type 1 congenital cystic adenomatoid malformation. A, Coronal fetal MR image shows hyperexpanded, high-signal lesion (arrows) in left lobe. Note lower signal in normal right lung (R). B, Chest radiograph after birth shows lucent, multi- cystic lesion in left lung with rightward mediastinal shift. C, CT soon after birth shows large, lucent, multicystic lesion in left lung. Chest • 37 Later, and more commonly, the herniated vis- cera contain air and the hernia appears as an air-containing cystic mass. Less air-filled viscera in the abdomen than expected and an abnormal position of support apparatus, such as a nasogastric tube within a herniated stomach, are obvious clues that support the diagnosis (Fig. 3-17). Often a nasogastric tube becomes lodged at the esophagogastric junction because of the acute turn in the herniated stomach. This can be a supportive finding of the diagnosis. The diagnosis of CDH is commonly made prenatally by ultrasound and further evaluated by fetal MR imaging (Fig. 3-18A, B). The mortal- ity rate for CDH is related to the degree of pul- monary hypoplasia. Systems of calculating lung volumes and predicting mortality have been devised for use with fetal ultrasound, fetal MR imaging, and postnatal radiography. Radiographic predictors of poor prognoses include lack of aerated ipsilateral lung, low per- centage of aerated contralateral lung, and severe mediastinal shift. Treatment includes support of respiratory failure, often by high-frequency ven- tilation or ECMO and surgical repair. The reported mortality rates associated with CDH range from 12% to 50%. One factor contributing to mortality is the presence of associated abnormalities, which are reported in a high per- centage of infants born with CDH. One report suggests that as many as 50% of patients with CDH have associated congenital heart disease. By the nature of the herniated bowel into the chest, most patients with CDH have associated malrotation. A V F F C BA FIGURE 3-16. Mixed lesion with components of both CCAM and sequestration seen at pathology. A, Chest radiograph obtained for multiple infections in young child shows bandlike opacity (arrow) in left lower lobe. It had been present on multiple radiographs. B, CT scan shows multicystic, air-filled lesion (arrow) in left lower lobe, suggestive of CCAM. C, CT reformat shows systemic arterial feeder (F) arising from aorta (A) and extending into lesion. Findings are characteristic of sequestration. Note draining pulmonary vein (V). 38 • Pediatric Imaging: The Fundamentals Sequestration The term pulmonary sequestration refers to an area of congenital abnormal pulmonary tissue that does not have a normal connection to the bronchial tree. The characteristic imaging fea- ture of sequestration is the demonstration of an anomalous arterial supply to the abnormal lung via a systemic artery arising from the aorta (Fig. 3-19A-C). All modalities that can demonstrate this abnormal systemic arterial supply, including MR imaging, helical CT, ultra- sound, and arteriography, have been advo- cated in making the diagnosis of sequestration. However, contrast-enhanced helical CT is pre- ferred because it both visualizes the systemic arterial supply when a sequestration is present (see Fig. 3-19) and further characterizes the lung abnormality if a sequestration is not present. Sequestration most commonly presents with recurrent pneumonia, usually in late childhood. Other presentations include a prenatally diag- nosed lung mass or respiratory distress in the newborn period. Because sequestrations do not communicate with the bronchial tree unless they become infected, they usually appear as radiopaque masses during the neona- tal period. After infection has occurred, air may be introduced and sequestration may appear as a multiloculated cystic mass. The most common location is within the left lower lobe. There has been much discussion concern- ing differentiation between intralobar and extra- lobar sequestrations. Extralobar sequestrations have a separate pleural covering, whereas intra- lobar sequestrations, which are more common, do not; however, the presence or absence of an extrapleural covering cannot be determined at imaging. Extralobar sequestrations are asso- ciated with other abnormalities in 65% of S FIGURE 3-17. Congenital diaphragmatic hernia. Radiograph shows stomach (S) containing tip of nasogastric tube (arrow) in left hemithorax. There is no visualized aerated bowel in the upper abdomen. There is mediastinal shift to the right. Contralateral lung is well-aerated. B A FIGURE 3-18. Congenital diaphragmatic hernia. A, Fetal MR image in coronal plane shows high signal content in multiple bowel loops (arrows) in left hemithorax. B, Chest radiograph after birth shows multiple bubblelike lucencies in left hemitho- rax. Note that in this case the stomach and nasogastric tube tip are not in the hernia. There is mediastinal shift to the right. The left upper lobe and right lung are well-aerated. Chest • 39 cases, whereas intralobar sequestrations are not. Differences in venous drainage patterns between intra- and extralobar sequestrations have been emphasized as a differentiating fac- tor but are actually variable with both types. The differentiation between intra- and extralobar sequestration cannot be made at imaging and does not affect surgical management. Visualization of the supplying systemic artery is the characteristic finding and is the documen- tation the surgeons are looking for prior to surgically removing the lesion. Bronchogenic Cyst Bronchogenic cysts occur secondary to abnormal budding of the tracheobronchial tree during development and occur in the lung parenchyma or the middle mediastinum. Mediastinal lesions are reportedly more common, making up between 65% and 90% of cases of bronchogenic cysts. When broncho- genic cysts occur in the lungs, they are most com- monly central in location, often in a perihilar distribution. Bronchogenic cysts are almost always solitary lesions; multiple bronchogenic cysts are very uncommon. Because of the pro- pensity for middle mediastinal and perihilar locations, compression of the distal trachea or bronchi is not an uncommon presentation. Air trapping in the lung distal to the lesion can occur. Like sequestrations, they do not contain air until they become infected and therefore may appear as well-defined soft tissue attenuation or cystic air-fluid-containing masses (see Fig. 2-11). B C A FIGURE 3-19. Sequestration. A, Chest radiograph obtained for repeated infections shows right lower lobe asymmetric opacity. B, CT shows feeding systemic arterial supply (arrows) arising from aorta and extending to lesion in right lower lobe. C, CT at lung windows shows right lower lobe air-filled cystic lesion. The air-filled cysts raise the possibility of a mixed CCAM/sequestration lesion. Again noted is the systemic arterial supply (arrow). 40 • Pediatric Imaging: The Fundamentals They can be quite large. They appear as well-defined cystic structures on imaging (see Fig. 2-11). ROLES OF IMAGING IN PEDIATRIC PNEUMONIA Respiratory tract infection is the most common cause of illness in children and continues to be a significant cause of morbidity and mortality. Evaluation of suspected community-acquired pneumonia is one of the most common indica- tions for imaging in children. Because of the frequency with which this scenario arises, knowl- edge of the issues concerning the imaging of chil- dren with community-acquired pneumonia is important. The roles of imaging in these children are multiple: confirmation or exclusion of pneu- monia, characterization and prediction of infec- tious agents, exclusion of other cause of symptoms, evaluation when there is failure to resolve, and evaluation of related complications. Confirmation or Exclusion of Pneumonia Making the diagnosis of pneumonia and conse- quently deciding on treatment and disposition is a common but complex and difficult issue. The symptoms and physical findings in children with pneumonia are sometimes nonspecific, especially in infants and young children. Many children present with nonrespiratory symptoms, such as fever, malaise, irritability, headaches, chest pain, abdominal pain, vomiting, or decreased appetite. Findings on physical exam- ination are also less reliable in children than in adults because young children are less cooper- ative with exams and have smaller anatomy and smaller respiratory cycles. Because of the inac- curacy of physical examination, radiography is often requested to evaluate children with sus- pected pneumonia. Several studies have shown that in a large percentage of cases, findings on chest radiography change caregivers’ diagnoses and treatment plans (antibiotics, bronchodila- tors, and patient disposition) for children being evaluated for potential pneumonia. At our insti- tution, we obtain both a frontal and a lateral film in the evaluation of a child with suspected pneu- monia. It has been shown that obtaining both views increases the negative predictive value of chest radiography for pneumonia. In addition, some findings such as hyperinflation in an infant are much more easily evaluated on the lateral than on the frontal views (Fig. 3-20A, B). Characterization and Prediction of Infectious Agent The historic emphasis in textbooks and articles concerning pneumonia has been on radiograph- ic patterns that suggest a specific infectious B A FIGURE 3-20. Viral lower respiratory infection in a young child. A, Frontal view shows increased perihilar markings and bandlike density (arrow) in right middle lobe, representing subsegmental atelectasis. B, Lateral view better shows marked hyperinflation with flattened hemidiaphragms, increased anterior-to-posterior diameter of the chest (chest is wider than it is tall), and barrel shape of chest. Increased perihilar markings make hila appear prominent. Chest • 41 agent, such as staphylococcal or streptococcal pneumonia. However, because of the limited ways in which the lung can respond to inflam- mation, findings suggestive of a specific diagno- sis are usually not encountered in the radiograph of a child with suspected communi- ty-acquired pneumonia. The more general issue in the evaluation of suspected pneumonia is whether the infectious agent is likely to be bacteria or viral, which determines whether the patient should be placed on antibiotics. To answer this question it is helpful to review the epidemiology of lower respiratory infections in children, the classic radiographic patterns of viral and bacterial pneumonia in children, and what is known about the accuracy of chest radiography in differentiating viral from bacterial infection. The common causal agents of lower respi- ratory tract infections in children vary greatly with age. In all age groups, viral infections are much more common than bacterial infec- tions. In infants and preschool-age children (4 months to 5 years of age), viruses cause 95% of all lower respiratory tract infections. The epidemiology is much different in school- age children (6 to 16 years of age). In school-age children, although viral agents remain the most common cause of lower respiratory tract infec- tions, the incidence of bacterial infection by Streptococcus pneumoniae increases. What is most striking is that Mycoplasma pneumoniae, which is an uncommon cause of pneumonia in preschool infants and children, is the cause of approximately 30% of lower respiratory tract infections in school-age children. Therefore, the odds that a child should be administered antibiotics for a respiratory tract infection are greatly influenced by the child’s age. In addition, there has been a recent increase in the incidence of pneumonia secondary to multidrug-resistant Staphylococcus aureus infections. These can occur at any age. Viral infections affect the airways, causing inflammation of the small airways and peribron- chial edema. This peribronchial edema appears on radiography as increased peribronchial opa- cities—symmetric course markings that radiate from the hila into the lung (Fig. 3-21A, B; and see Fig. 3-20A, B). The central portions of the lungs appear to be ‘‘dirty’’ or ‘‘busy.’’ It is one of the most subjective findings in radiology. In addition, the combination of the bronchial wall edema, narrowed airway lumen, and necrotic debris and mucus in the airway leads to small airway occlusion. This results in both hyperinflation and areas of subsegmental ate- lectasis. Hyperinflation is evident on chest radiographs in children in the presence of hyperlucency, the depression of the hemidia- phragm to more than 10 posterior ribs, and the increased anterior-to-posterior chest diameter. Hyperinflation is often much better appreciated on lateral than on frontal radiographs in infants and small children (see Fig. 3-20). Subsegmental atelectasis appears as wedge-shaped areas of density, most commonly in the lower and mid B A FIGURE. 3-21. Viral lower respiratory illness in a young child. A, Chest radiograph at peak of illness shows ropy increased perihilar markings and areas of subsegmental atelectasis. B, Radiograph 5 days earlier in same child shows clear lungs with absence of increased perihilar markings. Note the difference between the two radiographs. 42 • Pediatric Imaging: The Fundamentals lung (see Fig. 3-20A, B). There are several ana- tomic differences that render small children more predisposed to air trapping and collapse secondary to viral infection than adults: small airway luminal diameter, poorly developed col- lateral pathways of ventilation, and more abun- dant mucus production. The misinterpretation of areas of atelectasis as focal opacities suspi- cious for bacterial pneumonia is thought to be one of the more common misinterpretations in pediatric radiology. In contrast to the airway involvement in viral pneumonia, bacterial pneumonia occurs secondary to inhalation of the infectious agent into the air spaces. There is a resultant progres- sive development of inflammatory exudate and edema within the acini, resulting in consol- idation of the air spaces. On chest radiography, localized air space consolidation (Fig. 3-22) occurs with air bronchograms. The typical distri- bution is either lobar or segmental, depending on when in the course of development of the pneumonia the radiograph is obtained. Associated pleural effusions are not uncommon. Also, there is a propensity for pneumonia to appear ‘‘round’’ in younger children (Fig. 3-23). Round pneumonia is more common in children younger than 8 years of age and is most often caused by S. pneumoniae. The occurrence of this pattern is thought to be related to poor development of pathways of collateral ventilation. Round pneumonia tends to be soli- tary and occurs more commonly posteriorly and in the lower lobes. When such a lung mass is seen in a child with cough and fever, round pneumonia should be suspected. The child should be treated with antibiotics and the chest radiograph repeated. It is best to avoid unnec- essary CT examination in this clinical scenario. When a round opacity is seen in a child older than 8 years of age, other pathology should be suspected. Do these classic patterns of viral and bacterial infections accurately differentiate between children who have bacterial infection and need antibiotics and those who do not? Studies have shown that these radiographic patterns do have a high negative predictive value (92%) for excluding bacterial pneumo- nia. But the positive predictive value is low (30%). In other words, 70% of children who have radiographic findings of bacterial infec- tion actually have viral infection. In regard to decisions about administering antibiotics to children with suspected pneumonia, the goals are to treat all children who have bacterial pneumonia with antibiotics while minimizing the treatment of children with viral illnesses. Therefore, the high negative predictive value of chest radiography for bacterial pneumonia is useful in identifying those children who do not need antibiotics. P FIGURE 3-22. Bacterial pneumonia. Radiograph shows focal lung consolidation (P) in lateral aspect of right lower lobe, consistent with bacterial pneumonia. FIGURE 3-23. Round pneumonia. Radiograph shows rounded opacity overlying the left hilum. This is the location of the superior segment of the left lower lobe. Chest • 43 Exclusion of Other Pathologic Processes Many of the presenting symptoms of pneumonia in children are nonspecific, and the spectrum of presentations overlaps with a number of other pathologic processes involving the chest or other anatomic regions. Therefore, one of the other roles of chest radiography in the eval- uation of a child who potentially has pneumonia is the exclusion of other processes. Two areas that are often blind spots for radiologists and may be involved by conditions that mimic pneu- monia are the airway and the chest wall. Processes that cause extrinsic compression of the trachea and bronchi can mimic pneumonia by causing noisy breathing, lobar collapse, and recurrent infection. Evaluation of the diameter of the airway should be stressed as a routine part of evaluating radiographs. Rib abnormalities may be evidence that a lung opacity seen on chest radiography does not represent pneumo- nia. The presence of rib erosion or asymmetric intercostal spaces helps to differentiate neuro- blastoma from chest opacity secondary to pneumonia. Failure to Resolve Unlike in adults, in whom postobstructive pneu- monia secondary to bronchogenic carcinoma is a concern, follow-up radiography to ensure res- olution of radiographic findings is not routinely necessary in an otherwise healthy child. There is a tendency to obtain follow-up radiographs both too early and too often. Follow-up radiographs should be reserved for children who have persistent or recurrent symptoms and those who have an underlying condition such as immunodeficiency. The radiographic findings of pneumonia can persist for 2 to 4 weeks, even when the patient is recovering appropri- ately clinically. When follow-up radiographs are indicated, it is ideal to avoid obtaining them until at least 2 to 3 weeks have passed, if clinical symptoms allow. Causes of failure of suspected pneumonia to resolve include infected developmental lesions, bronchial obstruction, gastroesophageal reflux and aspiration, and underlying systemic disor- ders. The most common developmental lung masses that may become infected and present as recurrent or persistent pulmonary infection include sequestration and cystic adenomatoid malformation. These entities have been dis- cussed previously. Complications of Pneumonia The evaluation of complications related to pneu- monia can be divided into several clinical sce- narios: primary evaluation of parapneumonic effusions, evaluation of a child who has persis- tent or progressive symptoms despite medical or surgical therapy, and the chronic sequelae of pneumonia. PRIMARY EVALUATION OF PARAPNEUMONIC EFFUSIONS Parapneumonic effusions occur commonly in patients who have bacterial pneumonia. Multiple therapeutic options are available in the man- agement of parapneumonic effusions, including antibiotic therapy alone, repeated thoracentesis, chest tube placement, thrombolytic therapy, and thoracoscopy with surgical débridement. Great differences in opinion exist among care- givers regarding the timing and aggressiveness of management of parapneumonic effusions. Traditionally, the aggressiveness of therapy has been based on categorizing parapneumonic effu- sions as empyema or transudative effusion as determined by needle aspiration and analysis of the pleural fluid. Several imaging modalities have been advo- cated to differentiate empyema from transuda- tive effusion without the use of an invasive diagnostic thoracentesis, including decubitus radiographs, ultrasound, and CT. If there is a significant change in the position and appear- ance of the pleural fluid on the decubitus images as compared to the upright radiograph, the fluid is considered to be free flowing and nonloculated. If there is no change in position of the pleural fluid, the fluid is considered to be loculated (Fig. 3-24A-C). In my experience, these decubitus radiographs have been more confusing than helpful, and we do not advocate the use of decubitus radiographs to evaluate pleural effusions at our institution. On CT, find- ings such as thickening or enhancement of the parietal pleura and thickening or increased attenuation of the extrapleural fat were pre- viously thought to favor empyema over transu- dative effusion, but this has been shown to be inaccurate (Fig. 3-25A, B; and see Fig. 3-29). Ultrasound has also been advocated as an aid 44 • Pediatric Imaging: The Fundamentals in making therapeutic decisions for parapneu- monic effusions. In one study, parapneumonic effusions were categorized as low grade (anec- hoic fluid without internal heterogeneous echo- genic structures) or high grade (fibrinopurulent organization demonstrated by the presence of fronds, septations, or loculations) (see Figs. 3-24, 3-25). In children in whom effusions were high grade, hospital stay was reduced by nearly 50% when operative intervention was performed. The length of hospital stay in children with low-grade effusions was not affected by operative intervention. Therefore, ultrasound may play a more useful role than CT in the early evaluation of parapneumonic effusions. It is not uncommon for ultrasound to show multiple septations and in the same case to show no evidence of septations on CT (see Fig. 3-25). We currently advocate ultra- sound, rather than CT or decubitus radiographs, in the primary evaluation of parapneumonic effusions. EVALUATION OF PERSISTENT OR PROGRESSIVE SYMPTOMS When children exhibit persistent or progressive symptoms (fever, respiratory distress, sepsis) despite appropriate medical management of pneumonia, there is commonly an underlying suppurative complication. Potential suppurative complications include parapneumonic effusions such as empyema, inadequately drained effu- sions, and persistent effusion due to malposi- tioned chest tube; parenchymal complications, C BA FIGURE 3-24. Parapneumonic effusion (empyema) evalu- ated by decubitus radiographs and ultrasound. A, Radiograph shows pleural effusion (arrows) in child with pneumonia. B, Decubitus radiograph with left side down shows no change in pleural effusion (arrows), I think. Lack of change is supposed to suggest loculation, but is probably not that helpful a diagnostic tool. C, Ultrasound of left pleural fluid demonstrating multiple areas of septations (arrows) and debris—a high-grade effusion, predictive of benefit from aggressive drainage. Chest • 45 such as cavitary necrosis or lung abscess; and purulent pericarditis. Although chest radiogra- phy is the primary imaging modality for detect- ing such complications, a significant percentage of them are not demonstrated by radiography. In a child who has had a noncontributory radio- graph and who has not responded appropriately to therapy, contrast-enhanced CT has been shown to be useful in detecting clinically signif- icant suppurative complications. CT can help to differentiate whether there is a pleural or a parenchymal reason for persistent illness. Administration of intravenous contrast is vital to maximize the likelihood of detection and the characterization of both parenchymal and pleural complications. LUNG PARENCHYMAL COMPLICATIONS On contrast-enhanced CT, both noncompro- mised consolidated lung parenchyma and atelectasis enhance diffusely. Large areas of decreased or absent enhancement are indicative of underlying parenchymal ischemia or impend- ing infarction. Suppurative lung parenchymal complications include a spectrum of abnormal- ities, such as cavitary necrosis, lung abscess, pneumatocele, bronchopleural fistula, and pul- monary gangrene. The name given to the sup- purative process is determined by several factors, including the severity, distribution, con- dition of the adjacent lung parenchyma, and temporal relationship with disease resolution. Lung abscess represents a dominant focus of suppuration surrounded by a well-formed fibrous wall. Lung abscess is actually uncommon in otherwise healthy children and typically occurs in children who are immunocompro- mised. On contrast-enhanced CT, lung abscesses appear as fluid- or air-filled cavities with defin- able enhancing walls (Fig. 3-26). Typically, there is no evidence of necrosis in the surrounding lung. Pneumatocele is a term given to thin- walled cysts seen at imaging and may represent L B P A FIGURE 3-25. Parapneumonic effusion (empyema) evaluated by CT and ultrasound. A, CT shows left parapneumonic effusion. There are no findings to suggest empyema on CT. There are no septations seen by CT, which is typical. B, Ultrasound shows consolidated lung (L) with surrounding band of pleural fluid (arrows). Note multiple echogenic septations consistent with complex effusion. FIGURE 3-26. Lung abscess. Contrast-enhanced CT shows well- defined cavity (arrows) with enhancing wall and containing air- fluid level. 46 • Pediatric Imaging: The Fundamentals a later or less severe stage of resolving or healing necrosis (Fig. 3-27A-C). Cavitary necrosis is the most commonly encountered suppurative complication. It is characterized by a dominant area of necrosis of a consolidated lobe that is associated with a variable number of thin-walled cysts (Fig. 3-28). CT findings of cavitary necrosis include loss of normal lung architecture, decreased paren- chymal enhancement, loss of the lung-pleural margin, and multiple thin-walled cavities con- taining air or fluid and lacking an enhancing border (Fig. 3-29). Although historically described as a complication of staphylococcal pneumonia, cavitary necrosis was much more commonly seen as a complication of streptococ- cal pneumonia during the last decade. Cavitary necrosis in association with multi-drug-resistant S. aureus infection has been occurring with increased frequency recently (see Fig. 3-27). The presence of cavitary necrosis is indicative of an intense and prolonged illness. However, unlike in adults in whom the mortality rate in cavitary necrosis is high, and early surgical removal of the affected lung has been advo- cated, the long-term outcome for children with cavitary necrosis is favorable in most cases with medical management alone. It is amazing that in children with cavitary necrosis, follow-up radio- graphs obtained more than 40 days after the acute illness are most often normal or show only minimal scarring. It may sometimes be difficult on a single imaging study to differentiate a suppurative lung parenchymal complication of pneumonia from an underlying cystic congenital lung C BA FIGURE 3-27. Rapid development of necrosis and pneumato- cele formation in an infant with multi-drug-resistant S. aureus pneumonia. A, Radiograph obtained in the inten- sive care unit after intubation for respiratory failure shows patchy bilateral lung consolidation. Note position of PICC with tip in inferior aspect of superior vena cava (arrow). Note widening of soft tissues, consistent with anasarca. B, Radiograph 3 days later shows interval development of mul- tiple bilateral areas of necrosis and cyst formation. There is progressive anasarca. C. Radiograph taken 2 days after that shown in B shows progressive development of necrosis and cyst formation. Not that it matters, but because many of the cysts are thin-walled and without surrounding opacification, pneumatocele is acceptable terminology. Note the develop- ment of bilateral pneumothorax with left chest tube place- ment and progressive anasarca. Chest • 47 lesion that has become secondarily infected. Infected congenital cystic adenomatoid malfor- mations may appear very similar to cavitary necrosis. Obviously, historical imaging studies showing a lack of a cystic lesion exclude underlying CCAM, but such historical examina- tions often do not exist or are not available. Observable resolution of the cystic lesion on follow-up studies ensures that the lesion is no longer clinically relevant and makes cavitary necrosis much more likely. However, some CCAMs have been reported to scar down and resolve after becoming infected. CHRONIC LUNG COMPLICATIONS OF PNEUMONIA Acute pneumonia can lead to parenchymal damage and long-term sequelae. The most common sequelae of acute pneumonia are bronchiectasis and Swyer-James syndrome. Bronchiectasis is enlargement of the diameter of the bronchi that is related to damage to the bronchial walls. It is best demonstrated by high- resolution CT, where the diagnostic finding is that the bronchus in question is larger in diameter than the adjacent pulmonary artery (Fig. 3-30). Swyer-James syndrome is character- ized by unilateral lung hyperlucency that is thought to be secondary to a virus-induced nec- rotizing bronchiolitis that leads to an obliterative bronchiolitis (see Fig. 3-30). Radiography shows a hyperlucent and enlarged lung with a static lung volume. The pulmonary vessels are less prominent than on the normal side. Tuberculosis The incidence of tuberculosis in children has been increasing. Children with primary tubercu- losis can present with pulmonary consolidation within any lobe. It is often associated with FIGURE 3-28. Cavitary necrosis. Photograph of surgical specimen shows consolidated lung (tan area) with areas of necrosis and cavity formation (arrows). L P FIGURE 3-29. Cavitary necrosis with bronchopulmonary fistula formation. CT shows consolidation of the right lung. Portions of the lung demonstrate cavitary necrosis (arrows). There are also areas of consolidated lung that enhance (L) and are not compro- mised. There is a pleural effusion (P) that contains both air and fluid. There is thickening and enhancement of the parietal pleura (white arrowhead) and thickening of the extrapleural space (black arrowhead), both findings that claimed to be sug- gestive of empyema rather than transudative effusion but were shown to be inaccurate. FIGURE 3-30. Chronic complications related to recurrent pneu- monias. CT shows multiple round, soft tissue density lesions in medial right lower lobe (arrows) consistent with bronchiectasis with mucus plugging. In the left lower lobe, there is an area of air trapping (arrowheads) consistent with obliterative bronchio- litis. This area remained hyperlucent on expiratory images. 48 • Pediatric Imaging: The Fundamentals hilar lymphadenopathy or pleural effusion. Therefore, when lung consolidation is seen with associated lymphadenopathy or effusion in a child who is not acutely ill, there should be a high suspicion for tuberculosis. Most of the cases of pulmonary tuberculosis that I have seen have demonstrated unilateral hilar lym- phadenopathy (Fig. 3-31A, B). Such cases should be considered tuberculosis until proven otherwise. COMMON CHRONIC OR RECURRENT PULMONARY PROBLEMS IN SPECIAL POPULATIONS In children with certain underlying conditions, the clinical scenarios and differential diagnoses differ greatly from those seen in the general population. Commonly encountered scenarios include the evaluation of pneumonia in immu- nocompromised children, acute chest syndrome in children with sickle cell anemia, and pulmo- nary complications in children with cystic fibrosis. Pneumonia in Immunodeficient Children Children can be immunocompromised for a variety of reasons, including cancer therapy, bone marrow transplantation, solid organ trans- plantation, primary immunodeficiency, and AIDS. This is a population that continues to increase. Acute pulmonary processes are a common cause of morbidity and mortality in these patients. As with immunocompetent chil- dren, radiography is the primary modality used to confirm or exclude pneumonia. However, because many of the chest radiographs obtained in these children are portable and because of the consequences of missing an infection, CT plays a greater role in evaluating for an acute pulmo- nary process when chest radiographs are non- contributory. I would guess that in many tertiary institutions the number of chest CTs obtained in immunocompromised children is greater than the number of those obtained in immuno- competent children. In immunocompetent children, the main question is whether a pulmonary process is viral or bacterial; in immunocompromised children, there are many more possible causes of acute pulmonary processes They include alveolar hemorrhage, pulmonary edema, drug reaction, idiopathic pneumonia, lymphoid inter- stitial pneumonitis, bronchiolitis obliterans, bronchiolitis obliterans with organizing pneu- monia, and chronic graft-versus-host disease. The CT findings for many of these entities are overlapping and nonspecific. A clinical question often posed is this: Is there evidence of fungal infection? The hallmark CT finding indicating fungal infection is the presence of nodules B A FIGURE 3-31. Tuberculosis in a 7-year-old boy. A and B, Frontal and lateral radiographs of the chest demonstrate a left hilar mass (arrows) consistent with unilateral lymphadenopathy. There is also left upper lobe collapse. Note displaced major fissure on lateral view (arrowheads). Chest • 49 (Figs. 3-32A, B, 3-33). They are commonly clus- tered and may exhibit poorly defined margins, cavitation, or a surrounding halo that has the opacity of ground glass. However, many of these findings are also nonspecific. In these cases CT does aid in directing potential interven- tions, such as bronchoscopy or percutaneous lung biopsy, to high yield areas. Acute Chest Syndrome in Sickle Cell Anemia Children with sickle cell anemia can develop acute chest syndrome, which is manifested by fever, chest pain, hypoxia, and pulmonary opacities on chest radiographs (Fig. 3-34). Acute chest syndrome is much more common in children than adults with sickle cell anemia. It occurs most commonly between 2 and 4 years of age and is the leading cause of death (25% of deaths) and the second most common cause of hospitalization in those affected with sickle cell anemia. Although it is debated whether the cause of such episodes is more often related to infection or infarction, many believe the lung opacities are related to rib infarction, splinting, and subsequent areas B A FIGURE 3-32. Fungal pneumonia in child after bone marrow transplantation for aplastic anemia. A, CT shows poorly defined nodules and associated ground-glass opacity. B, A CT taken earlier shows clear lungs. Note the striking change since this baseline study. FIGURE 3-33. Histoplasmosis infection. CT shows multiple nodules bilaterally. There is a biopsy site on the left, anteriorly. A B C FIGURE 3-34. Acute chest syndrome in a 6-year-old boy with sickle cell anemia. A, Chest radiograph obtained at admission shows low lung volumes and minimal focal opacity within the left lower lobe. B, Chest radiograph obtained 1 day later shows consolidation of a large portion of the left lung. C, Chest radio- graph obtained 2 days after A shows complete left lung opacification. 50 • Pediatric Imaging: The Fundamentals of atelectasis. Radiography often shows segmen- tal to lobar pulmonary opacities but can also be normal. There can be an associated increase in cardiomegaly. Bone scans may show rib infarcts. The children are treated with oxygen, antibiotics, and pain control, and the pulmonary opacities are commonly monitored by radiography. Cystic Fibrosis Cystic fibrosis is a genetic disease that most com- monly affects the respiratory and gastrointestinal tracts. In the respiratory system, abnormally vis- cous mucus leads to airway obstruction and infection that causes bronchitis and bronchiecta- sis. Children may initially present with recurrent respiratory tract infections. Radiography may be normal at young ages but eventually demon- strates hyperinflation, increased peribronchial markings, mucus plugging, and bronchiectasis. The hilar areas can become prominent because of a combination of lymphadenopathy second- ary to the chronic inflammation and enlarged central pulmonary arteries related to the devel- opment of pulmonary arterial hypertension. Chest radiography is used to monitor the disease and evaluate for complications during acute exacerbations. Such complications include focal pneumonia, pneumothorax, and pulmo- nary hemorrhage. To monitor the progression of disease, some institutions use high-resolution CT, which demonstrates findings such as bron- chiectasis and bronchial wall thickening in greater detail and earlier than does radiography (Fig. 3-35). HIGH-RESOLUTION CT IN CHILDREN WITH QUESTIONED CHRONIC ASPIRATION One of the more common indications for high- resolution CT in the pediatric population is ques- tioned chronic aspiration. Often this issue arises in children with neurologic abnormalities such as cerebral palsy or chronic tracheotomy tubes when decisions about methods of feeding are being entertained. High-resolution CT findings of chronic aspiration include bronchiectasis, tree-in-bud opacities (Fig. 3-36A, B), and increased interstitial linear opacities. Findings more often occur in lower lobes. Trauma RIB FRACTURES AND LUNG CONTUSION There is a greater component of cartilage than bone within the chest walls of children, so there is more compliance than there is in the chest walls of adults. Because of this increased com- pliance, the sequelae of trauma to the pediatric chest are unique in several ways. First, the inci- dence of rib fractures after high-speed motor vehicle accidents is lower in children than in adults. Second, the deceleration forces of high speed collisions are more likely to be dispersed into the lung in children, resulting in lung con- tusion. Children with lung contusions have been B A FIGURE 3-35. Cystic fibrosis. A, Radiograph shows areas of bron- chial wall thickening and bronchiectasis, most prominent in the right upper lobe. B, High-resolution CT shows diffuse bronchi- ectasis and bronchial wall thickening within the upper lobes. There are also multiple areas of poorly defined opacities, partic- ularly in the peripheral portions of the left upper lobe. These have a tree-in-bud appearance. Chest • 51 shown to have higher morbidity and mortality rates than those without lung contusions. Although chest CT is not commonly performed to evaluate for lung contusion, the lower lungs are often seen on CT when it is performed to evaluate for abdominal trauma. Characteristic findings in lung contusion on CT include non- segmental distribution, posterior location, cres- cent shape, and mixed confluent and nodular characteristics (Fig. 3-37). In children with small lung contusions, the compliance of the chest wall can result in a rim of nonopacified lung between the consolidated contusion and the adjacent ribs seen on CT (see Fig. 3-37). This subpleural sparing can be helpful in differ- entiating lung contusion from other causes of lung opacification. The CT finding that classifies an opacified area as a lung laceration rather than a lung contusion is the presence of a fluid- or air-filled cyst within the opacified lung (Fig. 3-38A, B; and see Fig. 3-37). These cystic spaces result from torn lung. Finally, the sites of rib fracture in children differ from those in adults. Rib fractures in young children in the absence of an obvious traumatic event are highly suspicious for child abuse (Figs. 3-39, 3-40A, B). Pediatric rib fractures are more likely to be posterior than lateral. In child abuse, as a result of squeezing an infant’s thorax, the posterior ribs can be excessively levered at the costotransverse process articulation, causing posterior fracture at this site. In the appropriately aged child, these findings are considered pathognomonic for child abuse. MEDIASTINAL INJURY The incidence of aortic injury is also much lower in children than in adults. This, in com- bination with the lower incidence of obesity in children as compared to adults, makes the uncleared mediastinum on a chest radiograph after trauma a much less common scenario in children than in adults. Otherwise, the use of CT and angiography and the imaging findings of aortic injuries are no different from those encountered in adults. HYDROCARBON INGESTION The aspiration of the hydrocarbons in gasoline, furniture polish, kerosene, or lighter fluid when young children get into and drink such liquids can cause a combination of chemical B A FIGURE 3-36. Aspiration. A, Radiograph in a child suspected of having aspiration shows increased nodular opacities in the right lung. B, High-resolution CT shows multiple nodular opa- cities (arrows) with tree-in-bud appearance. PTX FIGURE 3-37. Lung contusion and laceration after a motor vehi- cle accident. CT shows characteristic findings of contusion on the left, including posterior location, crescent shape, nonseg- mental distribution, and subpleural sparing (arrows). On the right, there is large pneumothorax (PTX) and consolidation of lung with an air-filled cyst (arrow) consistent with lung laceration. 52 • Pediatric Imaging: The Fundamentals pneumonitis and atelectasis secondary to surfac- tant destruction. Radiographic findings may not manifest for up to 12 hours after ingestion. However, a normal radiograph at 24 hours after suspected ingestion excludes significant aspiration. The lung opacities tend to be in the lung bases (Fig. 3-41) and may persist for weeks after clinical improvement. Pneumatoceles are not uncommon sequelae. Mediastinal Masses The mediastinum is the most common location of primary thoracic masses in children. Also, the majority of mediastinal masses occur in children rather than in adults. As in adults, characterizing the location of the mass as anterior, middle, or posterior mediastinal can focus the differential diagnosis of mediastinal masses (Table 3-4). ANTERIOR MEDIASTINUM By far the most commonly encountered issues in the anterior mediastinum are the normal thymus mistaken as a mass and lymphoma. There are a large number of other potential but much less common causes of anterior mediastinal masses in children. They include teratoma (and other germ cell tumors), thymoma, multilocular thymic cysts seen in association with AIDS, and thyroid enlargement and heterogeneity (often with calcifications) in Langerhan cell his- tiocytosis (in which lung cysts are also present; Fig. 3-42). B A FIGURE 3-38. Lung laceration following motor vehicle accident. A, Radiograph shows nonspecific opacification of right lower lobe. B, CT shows right lower lobe consolidation with air- and fluid-filled cavities (arrows) consistent with lung laceration. FIGURE 3-39. Child abuse. Radiograph shows healing fractures (arrows) of right fourth and fifth ribs. TABLE 3-4. Common Mediastinal Masses by Location Anterior Middle Posterior Normal thymus Lymphoma Teratoma Lymphadenopathy Duplication cyst Neuroblastoma Chest • 53 NORMAL THYMUS One of the most common areas of confusion in the imaging of children is related to differen- tiating the normal thymus from pathologic processes. This confusion led to thymic radia- tion therapy in the first half of the 20th century, when children with a normal prominent thymus on chest radiography were radiated because of the erroneous belief that a big thymus com- pressed the airway and predisposed to death. Distinguishing the normal thymus from disease continues to cause diagnostic problems today, particularly for those who do not often image children. In children, the thymus has a variable appearance in both size and shape. In children less than 5 years of age, and particularly in infants, the thymus can appear to be very large (Fig. 3-43). Large thymuses are said to be more common in boys. The thymus also has variable configurations. A number of names have become associated with normal variations in the thymus, such as the sail sign (Fig. 3-44), which refers to a triangular extension of the thymus, most commonly to the right, on frontal chest radiography. It resembles a sail. This should not be confused with the spinnaker sail B A FIGURE 3-40. Child abuse. A, Radiograph shows multiple fractures that occurred at different times. There are multiple subacute healing rib fractures (white arrows) with callus forma- tion, a subacute healing right clavicle fracture (arrowhead), and multiple acute right-sided rib fractures (black arrows) without callus formation. B, CT shows callus around healing rib frac- tures on left (arrows) and characteristic acute fracture of the pos- terior rib (arrowhead) on right. A rib fractures against the transverse process when a child is squeezed. FIGURE 3-41. Hydrocarbon aspiration in a 1-year-old boy who drank gasoline from an orange juice container on the family’s garage floor. Chest radiograph shows bibasilar lung consolida- tion. The patient is intubated. FIGURE 3-42. Enlarged thymus with calcifications in child with Langerhans cell histiocytosis. CT shows prominent thymus with high-attenuation calcifications. 54 • Pediatric Imaging: The Fundamentals sign (Fig. 3-45), which is an indication of pneu- momediastinum, in which the abnormally located air lifts the thymus up so it looks like the sail on the front of a racing boat. Between 5 and 10 years of age, the thymus becomes less prominent radiographically because of the disproportionately decreased growth of the thymus in relationship to the growth of the rest of the body. During a child’s second decade, the thymus should not be visualized as a discrete anterior mediastinal mass on chest radiography. Abnormality of the thymus (or anterior med- iastinum) is suspected when the thymic silhou- ette has an abnormal shape or an abnormal size in relationship to the patient’s age. Displacement or compression of the airway or other structures is suspicious for abnormality. CT, ultrasound, MR imaging, and fluoroscopy can be used to help differentiate the normal thymus from an abnormal mass, but CT is probably used most commonly. When CT is performed to eval- uate suspicious cases, the normal thymus should appear homogeneous in attenuation, typically is quadrilateral in shape in young children (Fig. 3-46) and triangular in teenagers (Fig. 3-47A, B), and may have slightly convex margins. Heterogeneity, calcification, and dis- placement or compression of the airway or vascular structures indicate an abnormality (Fig 3-48A-D; and see Fig. 3-42). True pathologic masses of the thymus are actually quite rare in children. Thymic rebound is another source of confu- sion concerning normal thymic tissue. After a patient has ceased receiving chemotherapy for a malignancy, it is normal for the thymus to grow back, as seen in serial CT examinations. Thymic volume has been shown to vary cyclically by as much as 40% during rounds of chemotherapy (see Fig. 3-47). This intervallic increase in soft tissue attenuation in the anterior mediastinum T T H FIGURE 3-43. Normal, prominent size of the thymus. Photograph from autopsy of an infant who died of sudden infant death syndrome shows frontal view of thymus (T) after thoracotomy. Note the prominent size of the thymus in relation to the heart (H). The thymus is bilobed. In this patient the left lobe is larger than the right. (Image courtesy Janet L. Strife, MD, Cincinnati, OH.) FIGURE 3-44. Normal, prominent thymus with ‘‘sail’’ sign. Radiograph shows prominent but normal thymus with right- ward triangular extension (arrow). FIGURE 3-45. ‘‘Spinnaker sail sign’’ in child with pneumomedi- astinum. Radiograph shows thymus (arrows) lifted off of medi- astinum by air in mediastinum. The uplifted thymus resembles a spinnaker sail. Chest • 55 should not be considered abnormal when encountered on cross-sectional imaging. LYMPHOMA Lymphoma is the third most common tumor in children, exceeded only by leukemia and brain tumors. It is by far the most common abnormal anterior mediastinal mass in children, particularly in older children and teenagers. Therefore, lymphoma is the working diagnosis for newly diagnosed anterior mediastinal masses in children. Age is helpful in differentiating a normal thymus from lymphoma because a normal thymus is most common in small chil- dren and lymphoma is most common in teen- agers. The most problematic case is the slightly prominent anterior mediastinum in a 10- year-old. One helpful clue in identifying lympho- ma is that mediastinal lymphoma is commonly associated with cervical lymphadenopathy. The most common types of lymphoma that involve the mediastinum include Hodgkin lymphoma and the lymphoblastic type of non- Hodgkin lymphoma. Both lesions can appear as discrete lymph nodes or as a conglomerate mass of lymph nodes, most commonly within the anterior mediastinum (see Fig. 3-48). Lung involvement, when present, is usually contiguous with mediastinal and hilar disease. Calcifications are rare in untreated lymphoma and when present should raise the possibility of other diagnoses such as teratoma (Fig. 3-50). Most mediastinal masses are initially identi- fied on chest radiography and then further eval- uated by CT, which confirms the presence of an anterior mediastinal mass, evaluates the extent of disease, and evaluates for potential complica- tions. The potential complications related to mediastinal lymphoma include airway compres- sion, compressive obstruction of venous struc- tures (superior vena cava, pulmonary veins), and pericardial effusion (see Figs. 3-48, 3-49). B A FIGURE 3-47. Thymic rebound in a child on chemotherapy. A, CT taken while the child was on chemotherapy shows little thymic tissue. B, CT taken 3 months later when child was off chemotherapy shows regrowth of thymus (arrows). Note the typical triangular shape of the thymus as is seen during teenage years. T FIGURE 3-46. Normal thymus on cross-sectional imaging. CT in a young child shows thymus (T) to be quadrilateral in shape, to have convex margins, and to be of homogeneous attenuation. There is no compression of the trachea or superior vena cava. 56 • Pediatric Imaging: The Fundamentals Airway compression is especially important because it may influence decisions concerning surgical biopsy with general anesthesia versus percutaneous biopsy with local anesthesia. If a patient cannot lie recumbent for CT imaging because of airway compression, the images can usually be obtained with the patient posi- tioned prone because the anterior mediastinal mass falls away from the airway. Compression of the airway by more than 50% from the expected round shape has been shown to be associated with a high risk for complications related to anesthesia. Because of this, some such mediastinal masses are biopsied using ultrasound guidance and local anesthesia. Middle Mediastinal Masses Middle mediastinal masses are less common than anterior or posterior mediastinal masses and are usually related to lymphadenopathy or D M C M BA FIGURE 3-48. Lymphoma. A, Frontal radiograph shows marked enlargement of superior mediastinum and associated right pleural effusion. B, Lateral radiograph shows posterior displacement, compression, and poor visualization of the trachea (arrow), further supporting the presence of an abnormal mediastinal mass. C, CT shows large anterior mediastinal mass (M) with compression and posterior displacement of trachea (arrow) and compression of the superior vena cava (arrowhead). Note right pleural effusion. D, Coronal CT again shows mass (M) and compression of superior vena cava (arrow). Chest • 57 duplication cysts. Lymphadenopathy can be inflammatory, most often secondary to granu- lomatous disease, such as tuberculosis or fungal infection; or to neoplastic growth secondary to metastatic disease or lymphoma. Duplication cysts can be bronchogenic (see Fig. 2-11), enteric, or neurenteric. Duplication cysts are well-defined masses that appear cystic on cross-sectional imaging. Neurenteric cysts, by definition, have associated vertebral anomalies. Pathologic pro- cesses related to the esophagus can also cause middle mediastinal abnormalities. Chronic for- eign bodies can erode through the esophagus and cause a middle mediastinal mass, typically in the cervical esophagus at the level of the tho- racic inlet (Fig. 3-51A, B). A dilatated esophagus resulting from achalasia or a hiatal hernia may also appear as a middle mediastinal mass on chest radiography. L L FIGURE 3-49. Lymphoma with pericardial effusion. CT image from level of heart in a child with an anterior mediastinal mass; on more superior images shows extension of lymphoma mass (L) inferiorly. Note adjacent pericardial fluid (arrowheads) and bilateral pleural fluid (arrows). M FIGURE 3-50. Teratoma. CT shows anterior mediastinal mass (M) that is of fat attenuation. B A FIGURE 3-51. Chronic esophageal foreign body presenting as dysphagia and stridor in a young child. A, Axial CT shows inflammatory mass at thoracic inlet. There is a linear metallic density (arrows) suspicious for an eroded, chronic foreign body from the upper esophagus. The trachea is compressed (arrow- head). B, Coronal CT shows dense oval structure (arrows) in an inflammatory mass. At surgical retrieval, the foreign body was found to be a sequin. 58 • Pediatric Imaging: The Fundamentals D M C B M A W FIGURE 3-52. Neuroblastoma. A, Radiograph shows a large mass in right upper hemithorax. There is widening (W) of the interspace between the right third and fourth ribs and erosion of the undersurface of the right third rib (arrow). The rib splaying and erosion document chest wall involvement and the posterior nature of the tumor. B, CT shows large mass (M) with compression of the trachea (arrow). The mass is so large it extends from anterior to posterior chest walls. C, MIBG scan shows avid uptake of radiotracer within the mass (arrows), consistent with a neurogenic tumor. D, Photograph taken during surgical resection shows a mass (M) arising from the posterior chest. Chest • 59 Posterior Mediastinal Masses There are a number of causes of posterior me- diastinal masses in children. They include neural crest tumor, neurofibroma, lateral menigocele, diskitis, hematoma, and extramedullary hemato- poiesis. However, just as anterior mediastinal masses in older children are considered to be lymphoma, the working diagnosis for posterior mediastinal masses in young children is neuro- blastoma until proven otherwise. NEUROBLASTOMA Neurogenic tumors (neuroblastoma, ganglio- neuroblastoma, ganglioneuroma) are the most common posterior mediastinal masses in child- hood. Neuroblastoma is discussed in detail in the genitourinary section. Approximately 15% of neuroblastomas occur in the posterior med- iastinum, most occurring before a child is 2 years of age. Most neuroblastomas are visible on frontal radiographs of the chest as a posterior opacity. The soft tissue mass is often surprisingly poorly visualized on the lateral view. There is fre- quently erosion, destruction, or splaying of the adjacent posterior ribs (Fig. 3-52A-D). These findings may be subtle, so whenever a posterior chest opacity is identified an effort should be made to look for rib erosion. The neuroforamina may appear enlarged on the lateral view, sec- ondary to intraspinal extension of the tumor. Calcifications are reported to be visible on chest radiography in as many as 25% of cases, although in my experience it is less than that. Cross-sectional imaging with CT or MR imaging confirms the presence of the tumor and evalu- ates extent of disease, particularly whether there is intraspinal extension. Thoracic neuroblasto- mas have better prognosis than abdominal neuroblastomas. Pediatric Chest Wall Masses A number of primary malignant processes can arise in the chest walls of children. They include Ewing sarcoma, Askin tumor (primitive neuroec- todermal tumor of the chest wall), and other sar- comas (Fig. 3-53). Most of these lesions present with painful enlargement of the chest wall. Metastatic involvement by neuroblastoma, lym- phoma, or leukemia is actually more common than are primary tumors. On imaging, all of these malignancies typically appear as nonspecific aggressive lesions with poorly defined margins that include bony destruction and pleural involvement. However, one must consider that as much as one third of children have variations in the configuration of the ante- rior chest wall, including asymmetric findings, such as tilted sternum (Fig. 3-54), prominent convexity of anterior rib or costal cartilage, prominent asymmetric costal cartilage, para- chondral nodules, or mild degrees of pectus excavatum or carinatum. It is common for these asymmetric variants to be palpated by M FIGURE 3-53. Undifferentiated sarcoma of the chest wall in a young child. CT shows soft tissue attenuation mass (M) invol- ving the anterolateral chest wall on right. FIGURE 3-54. Tilted sternum with prominent costal cartilage presenting as a palpable mass on physical exam. CT shows the sternum (arrowhead) to be tilted with respect to the horizontal right-to-left axis of the body. The right margin of the sternum is more anterior than the right. The associated anterior position of the right costal cartilage (arrow), a normal variant, caused the palpable finding on physical exam. 60 • Pediatric Imaging: The Fundamentals the pediatrician, parent, or patient, and because of the fear of malignancy, cross-sectional imag- ing is requested. In a previous study that reviewed CT and MR examinations performed to evaluate children with suspected chest wall masses, all of the palpable lesions that were asymptomatic were related to normal anatomic variations. Knowledge that such variations are common should be communicated to referring physicians and parents when imaging is being contemplated in a child with an asymptomatic chest wall ‘‘lump.’’ One of the most common abnormalities in chest wall configuration is pectus excavatum. Although the majority of associated problems due to this deformity are cosmetic, pectus defor- mities can cause chest pain, fatigue, dyspnea on exertion, palpitations, and restrictive lung dis- ease. When the deformities are severe, surgical repair can be performed. Pectus excavatum is commonly treated by a minimally invasive procedure called a Nuss procedure. Prior to the Nuss procedure, surgeons commonly request CT examination to document the Haller index, which quantifies the severity of the pectus deformity (Fig. 3-55). To calculate the Haller index, low tube current (mA) images are obtained through the level of the greatest degree of pectus deformity. The Haller index is equal to the transverse left-to-right diameter of the chest, divided by the anterior-to-posterior diameter. The greater the Haller index, the more severe the pectus. A patient with a Haller index greater than 3.2 is considered a surgical candidate. Suggested Readings Condon VR: Pneumonia in children, J Thorac Imaging 6:31-44, 1991. Donnelly LF: Maximizing the usefulness of imaging in children with community-acquired pneumonia, AJR 172:505-512, 1999. Donnelly LF, Klosterman LA: Subpleural sparing: a CT find- ing of lung contusion in children, Radiology 204:385-387, 1997. Donnelly LF, Frush DP: Abnormalities of the chest wall in pediatric patients, AJR 173:1595-1601, 1999. Donnelly LF, Frush DP: Localized lucent chest lesions in neonates: causes and differentiation, AJR 172:1651-1658, 1999. Griscom NT: Respiratory problems of early life now allowing survival into adulthood: concepts for radiologists, AJR 158:1-8, 1992. Griscom NT, Wohl MB, Kirkpatrick JA: Lower respiratory infections: how infants differ from adults, Radiol Clin North Am 16:367-387, 1978. Kunisaki SM, Barnewolt CE, Estroff JA, et al: Large fetal con- genital cystic adenomatoid malformations: growth trends and patient survival, J Pediatr Surg 42:404-410, 2007. Merton DF: Diagnostic imaging of mediastinal masses in children, AJR 158:825-832, 1992. Swischuk KE, John SD: Immature lung problems: can our nomenclature be more specific? AJR 166: 917-918, 1996. Singleton EB: Radiologic consideration of intensive care in the premature infant, Radiology 140:291-300, 1981. FIGURE 3-55. Pectus excavatum. CT shows severe concavity of anterior chest wall. White lines are the anterior-to-posterior and left-to-right diameters of the chest. These are measured to calcu- late the Haller index, a quantitative measure of pectus severity. Chest •