Pediatric Chest

PEDIATRIC CHEST

Congenital Cystic Adenomatoid Malformation (CCAM) Background: CCAM is a developmental hamartomatous abnormality of the lung with adenomatoid proliferation of cysts resembling bronchioles. CCAM represents approximately 25% of all congenital lung lesions.

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Pathophysiology: CAM is believed to result from focal arrest in fetal lung development before the seventh week of gestation secondary to a variety of pulmonary insults. Depending on the time and type of insult, 4-26% of cases can be associated with other congenital abnormalities. However, arrest of pulmonary development with distortion of architectural differentiation may take place at any stage of embryonic development.

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CAM differs from normal lung tissue because of a combination of increased cell proliferation and decreased apoptosis. A welldefined intrapulmonary bronchial system is lacking, and normally formed bronchi supplying the mass are absent.

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Usually, the radiographic pattern appears as an expansile soft-tissue mass containing multiple air-filled cystic masses of varying size and shifting of the mediastinum. Initially and early in life, a homogeneous fluid-opacity pulmonary mass may present and evolve to demonstrate an air-filled cystic radiographic appearance over time. The initial dense appearance is a result of delayed emptying of alveolar fluid either via the bronchi or lymphatic and circulatory systems. In patients with CAM, the pattern in the lung demonstrates multiple radiolucent areas that vary greatly in size and shape. Cysts are separated from each other by strands of opaque pulmonary tissue. The involved lung may appear honeycombed or spongy, but occasionally, 1 large cyst may overshadow the others. Airtrapping within cystic spaces can cause rapid enlargement of the CAM and subsequent respiratory embarrassment. Findings are usually apparent in a symptomatic individual, but they may not be as apparent in an asymptomatic child.

Congenital Diaphragmatic Hernia (CDH) Background: (CDH) constitutes a major surgical emergency in the newborn, and the key to survival lies in prompt diagnosis and treatment. Symptoms depend on the degree of herniation; small hernias may initially pass unnoticed, whereas larger ones produce immediate and severe respiratory distress. Classification of CDH The left-sided Bochdalek hernia is seen in approximately 90% of cases. The major problem in a Bochdalek hernia is the posterolateral defect of the diaphragm, which results in either the failure of the pleuroperitoneal folds to develop or the improper or absent migration of the diaphragmatic musculature. Bilateral Bochdalek hernias are rare. The Morgagni hernia is a less-common CDH, occurring in only 5-10% of cases of CDH. This hernia occurs in the anterior midline through the sternocostal hiatus of the diaphragm, with 90% of cases occurring on the right side. A congenital hiatus hernia is very rare in neonates. In this form, hernia of stomach occurs through the esophageal hiatus Radiologic features The classic radiographic appearance is one which the left hemithorax is filled with cystlike structures (loops of bowel), the mediastinum is shifted to the right, and the

abdomen is relatively devoid of gas (Swischuk, 1997). In some cases, a few loops of intestine can be seen in the abdomen, but more often, only the stomach remains visible within the abdomen.

Hyaline Membrane Disease Background:Respiratory distress syndrome (RDS), also known as hyaline membrane disease (HMD), is an acute lung disease of the newborn caused by surfactant deficiency. It is seen primarily in neonates younger than 36-38 weeks' gestational age and weighing less than 2500 g. In comparison, HMD tends to occur in neonates younger than 32 weeks' gestational age and weighing less than 1200 g. The incidence and severity of RDS is inversely related to gestational age. RDS is the most common cause of respiratory failure during the first days after birth. In addition to prematurity, other factors contributing to the development of RDS are maternal diabetes, cesarean delivery without preceding labor, fetal asphyxia, and being the second born of twins. Pathophysiology: RDS is the result of anatomic pulmonary immaturity and a deficiency of surfactant. Pulmonary surfactant synthesis, in type II pneumocytes, begins at 24-28 weeks of gestation, and gradually increases until full gestation. Pulmonary surfactant decreases surface tension in the alveolus during expiration, allowing the alveolus to remain partly expanded, thereby maintaining a functional residual capacity.

In premature infants, an absence of surfactant results in poor pulmonary compliance, atelectasis, decreased gas exchange, and severe hypoxia and acidosis. Premature infants must expend a great deal of effort to expand their lungs with each breath, and respiratory failure ensues. RADIOGRAPH Classic findings In RDS, the classic chest radiographic findings consist of pronounced hypoaeration, bilateral diffuse reticulogranular opacities in the pulmonary parenchyma, and peripherally extending air bronchograms. The reticulogranularity is due to superimposition of multiple acinar nodules caused by atelectatic alveoli. The development of air bronchograms depends on the coalescence of areas of acinar atelectasis around aerated bronchi and bronchioles. In nonintubated infants, cephalic doming of the diaphragms and hypoexpansion are observed.

Bronchopulmonary Dysplasia Background: Bronchopulmonary dysplasia (BPD) is a chronic pulmonary disorder that results from the use of high positivepressure mechanical ventilation and high concentration oxygen in neonates with respiratory distress syndrome (RDS). It is defined as oxygen dependence at 28 days. BPD is pathologically characterized by inflammation, mucosal necrosis, fibrosis, and smooth muscle hypertrophy of the airways. With advances in medical management, BPD has

become the most common cause of chronic lung disease (CLD) in children. The following factors play a role in the development of BPD: •

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Preterm delivery (immature lungs): The disease is common in children delivered before 32 weeks' gestation and in those weighing less than 1000 g. High oxygen concentration (free radical–induced lung damage worsened by deficient antioxidants): A high oxygen concentration is an etiologic factor in patients with immature lungs, and any concentration greater than 60% is associated with a high incidence of the disease. Mechanical ventilation (large tidal volume and reduced lung compliance) RDS that requires mechanical ventilation: Sustained positive-pressure ventilation in preterm infants with RDS results in dilatation of the terminal bronchioles, which causes ischemic necrosis of the distal airways. Resultant pulmonary interstitial emphysema (PIE) and pneumothorax produce chronic lung damage. Although mechanical ventilation in RDS may be the original cause, it also occurs in patients with diaphragmatic hernia, persistent pulmonary hypertension of the newborn, meconium aspiration, and other diseases that require prolonged mechanical ventilation. RDS is not an absolute requirement for the development of BPD because the disease can occur in those receiving mechanical ventilation to manage other diseases.

Stages of radiographic changes

Pathophysiology: Immature lungs are underdeveloped and lack adequate surfactant to keep the alveolar ducts and early alveoli open on inspiration and expiration. The resulting diminished surface for transfer of gas and widespread atelectasis leads to inadequate transfer of carbon dioxide and oxygen across the epithelial surfaces to the pulmonary microvascular system. Methods to improve oxygen saturation include administering high concentrations of oxygen and expanding and maintaining that expansion of gas-exchanging surfaces of the lung using high levels of inhaled oxygen and positive pressure ventilation.

Four stages of radiographic changes of BPD have been described: stage I, which is RDS seen in the first week; stage II, which includes generalized haziness and plethora in the second week; stage III, which involves cystic changes and stranding in the third week; and stage IV, which is characterized by hyperinflation, extensive stranding, and an enlarged heart in the fourth week.

Excessive intra-airway pressure may lead to leak from the alveolar ducts (primordial acini) into the lung interstitium. Once in the interstitium, the gas is picked up in the rich lymphatic network of the neonate and carried toward the pleural lymphatics and central bronchopleural lymphatics. PIE usually occurs early during ventilation, and most infants present in the first 72 hours with this abnormality.

Pulmonary Interstitial Emphysema

It is observed less frequently now because of treatment of immature babies with exogenous surfactant, which improves compliance of the lung (thus less ventilatory pressure is needed) and keeps the alveolar ducts open during both inspiration and expiration. It also assists in the recruitment of alveolar ducts to prevent areas of overinflation and underinflation. Currently, PIE is seen more often in infants on long-term ventilator therapy with uneven aeration and bronchopulmonary dysplasia (BPD) leading to air trapping and potential airspace rupture.

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Infectious agents (eg, Ureaplasma urealyticum): U urealyticum is the most common infectious agent responsible for BPD, producing early and severe changes of BPD within 3 weeks. Other bacterial and fungal agents are also implicated.

Findings: Radiography is the mainstay imaging test for the diagnosis of BPD.

Background: Pulmonary interstitial emphysema (PIE) is an iatrogenic pulmonary condition of the premature infant with immature lungs. PIE occurs almost exclusively with mechanical ventilation. The ventilatory pressure used to keep the alveolar ducts open also may cause rupture of the alveolar duct (usually at the junction of the bronchiole and alveolar duct) and consequent escape of air into the pulmonary interstitium, lymphatics, and venous circulation.

Findings: Radiography indicates linear, oval, and occasional spherical cystic air-containing spaces throughout the lung parenchyma. The interstitial changes are initially linear but may become more cystic as the air in the interstitium congregates locally. Subpleural cysts also develop and may rupture to produce a pneumothorax. The heart tends to get smaller as intrathoracic pressure increases and results in diminished venous return into the chest. Overall lung volume is increased; however, the lungs are less compliant because they are splinted at a large volume by the air within the interstitium. Gas exchange is reduced by the increase in distance between the pulmonary vascular bed and the airspaces.

Transient Tachypnea of the Newborn Background: Transient tachypnea of the newborn appears soon after birth. It may be accompanied by chest retractions, by expiratory grunting, or by cyanosis. (This last manifestation can be relieved with minimal oxygen.) Recovery usually is complete within 3 days. Radiologically, this syndrome frequently is termed wet lung disease. In the medical literature, discussions concerning transient tachypnea of the newborn also can be found under the following names: retained fetal lung liquid, retention of fetal lung fluid, respiratory distress syndrome type II, transient respiratory distress of the newborn, and neonatal retained fluid syndrome. Pathophysiology: During fetal life, the lungs are expanded with an ultrafiltrate of the fetal serum. In the course of neonatal

transition, this ultrafiltrate must be removed and replaced with air. The classic explanation for how this occurs was that passage through the birth canal would, by squeezing the thorax, help eliminate the liquid in the lungs, with the remaining fluid being removed by pulmonary capillaries and the lymphatics. Currently, however, the bulk of this clearance is thought to be mediated by transepithelial sodium reabsorption through sodium channels in the alveolar epithelial cells, with only a limited contribution from mechanical factors and Starling forces. Changes in the hormonal milieu of the fetus and its mother, brought about mainly by the onset of spontaneous labor, prepare the fetus for the neonatal transition to air breathing. Transient tachypnea of the newborn occurs when the liquid in the lung is removed slowly or incompletely; this phenomenon correlates with a decreased thoracic birth squeeze or diminished respiratory effort in the newborn. Transient tachypnea has been identified as occurring with cesarean birth and infant sedation. Longer labor intervals, macrosomia of the fetus, and maternal asthma also have been associated with a higher frequency of transient tachypnea of the newborn. Findings: Findings on chest radiographs may include mild, symmetrical lung overaeration; prominent perihilar interstitial markings; and small pleural effusions. Occasionally, the right side may appear more opacified than the left. Radiographic appearance at times can mimic the diffuse, granular appearance of hyaline membrane disease but without pulmonary underaeration. Neonates with transient tachypnea

usually are at term. Radiographic lung changes also may resemble the coarse, interstitial pattern of other causes of pulmonary edema or the irregular pattern of lung opacification seen in meconium aspiration syndrome.

Meconium Aspiration Background: The term meconium is derived from ancient Greek word meconium-arion, or opium-like, from the Greek word mekoni meaning poppy juice. In the time of Aristotle, the term was used because it was believed that the substance induced fetal sleep. Pathophysiology: Passage of meconium into amniotic fluid most often represents a normal maturational event. However, in many instances, it may occur in response to fetal hypoxia or acidosis. Meconium passage likely requires neural stimulation of a mature gastrointestinal tract, without which there is no peristalsis and relaxation of the rectal sphincter. This may explain why meconium is rarely found in the amniotic fluid before 34 weeks' gestation. Meconium aspiration syndrome chiefly affects infants at term and afterward. The amniotic fluid and meconium mix to form a greenish-black fluid of variable thickness, or viscosity. Meconium aspiration syndrome occurs when the newborn aspirates the meconium-containing amniotic fluid. In addition to obstruction of the airway, the aspiration leads to an inflammatory response in the lung parenchyma (chemical pneumonitis). It is this inflammation, not the meconium itself, that results in the patchy infiltrates seen on chest radiography.

It is not clear which component(or components) of meconium triggers the inflammatory response. However, bile and liver enzymes have been suggested as the causative agents. Chest radiography typically shows hyperinflation with patchy opacities. These findings represent areas of atelectasis mixed with areas of air trapping. As mentioned above, air leaks are common, leading to pneumothorax, pneumomediastinum, pneumopericardium, and/or pulmonary interstitial emphysema. Pleural effusions may be present.

Epiglottitis Background: Epiglottitis is the inflammation of the supraglottic structures. In most cases, the condition is caused by a rapidly developing bacterial infection of the epiglottis, which has the potential to cause abrupt airway obstruction. Traditionally, this infection was most commonly caused by Haemophilus influenzae type b (HIB), though Streptococcus pneumoniae, Staphylococcus aureus, and group A betahemolytic streptococci were occasionally found. Sex: Epiglottitis is more common in males than females, with a male-to-female ratio of about 3:1. Age: Before widespread use of the HIB vaccine, epiglottitis occurred mainly in young children, peaking between 2 and 7 years of age. The disease is now rarely seen among children.

RADIOGRAPH Findings: On plain radiographs, the normal epiglottis is a thin, curved, flap of soft tissue opacity that is separated from the base of the tongue by air in the valleculae In epiglottitis, images show diffuse soft-tissue swelling with enlargement of the epiglottis and also of the normally thin aryepiglottic folds. One should look for an enlarged epiglottis (thumbprint sign), thickened aryepiglottic folds, and ballooning of the hypopharynx, usually with normal subglottic structures, although a rare case of supraglottitis may cause infraglottic swelling

Croup Background: Croup is a generic term encompassing a heterogeneous group of relatively acute conditions (mostly infectious) characterized by a syndrome of distinctive brassy coughs. These may be accompanied by inspiratory stridor, hoarseness, and signs of respiratory distress resulting from laryngeal obstruction. The word croup derives from an old Scottish term roup, which means "to cry out in a shrill voice." The most common form of croup is acute laryngotracheobronchitis or viral croup, an infection of both the upper and lower respiratory tracts. A reactive inflammatory response causes subglottic edema. Age: Viral croup is most common in patients aged 6 months to 5 years, with a peak incidence in the second year of life. Croup

is rare in the first 6 months of life. Stridor presenting in the first 6 months of life should initiate a search for other causes of stridor. Congenital anomalies and subglottic hemangiomas are other conditions to consider that narrow the airway and cause stridor in infants. The youngest reported child with croup was aged 3 months. RADIOGRAPH •

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Frontal neck radiograph: The lateral walls of the subglottic larynx normally are convex or shouldered. Wall edema in croup narrows this space with loss of lateral convexity, creating a steeple shape below the vocal cords. The narrowing may extend for 5-10 mm below the vocal cords. Lateral neck radiograph: The hypopharynx is overdistended during inspiration, and the subglottic region is hazy as a result of narrowing of the airway by mucosal edema. The larynx airway is indistinct. The undersurface of the vocal cords normally identified during phonation is not well identified. The epiglottis, aryepiglottic folds, and prevertebral spaces appear normal.