Recognizing Pediatric Diseases

Transient Tachypnea of the Newborn (TTN)

• Occurring in infants born by Caesarian or precipitous vaginal delivery, transient tachypnea of the newborn is the most common cause of respiratory distress in the newborn. It is thought to be due to delay in the resorption of fetal lung fluid.

• Clinically, TTN is marked by the immediate onset of tachypnea and mild respiratory distress. Intubation is usually not required. Infants typically improve over several hours with noninvasive oxygen supplementation and supportive therapy and completely recover by 48 hours.

Important Points

• Imaging findings of TTN:

  • The lungs are often hyperinflated, though less so in premature infants .

  • There can be streaky, perihilar linear densities.

  • There also may be fluid in the fissures and/or laminar pleural effusions ( Fig. 27.1 ).

Neonatal Respiratory Distress Syndrome

• Neonatal respiratory distress syndrome (NRDS) is a disease of premature infants , usually less than 34 weeks of gestation. The incidence and severity of the disease often worsens with increasing prematurity. There are numerous risk factors, including perinatal asphyxia, hypoxia, and maternal diabetes.

• The major cause of this disorder is surfactant deficiency. Without surfactant, the alveolar sacs have an increased tendency to collapse, leading to widespread atelectasis.

• Typically, these premature infants have severe respiratory distress after birth that progressively worsens. Clinical findings include cyanosis, grunting, nasal flaring, intercostal and subcostal retractions, and tachypnea.

Important Points

• Imaging findings of NRDS ( Fig. 27.2 ):

  • There is typically a diffuse ground-glass or finely granular appearance to the lungs in a bilateral and symmetric distribution. The granularity seen in the lungs is the interplay of air-distended bronchioles and ducts against a background of atelectatic alveoli.

  • Air bronchograms are common and extensive, especially extending peripherally.

  • Hypoaeration is seen in nonmechanically ventilated lungs. Hyperinflation in nonintubated patients excludes NRDS.

  

• Oxygen requirements progressively increase over the first few hours after birth. The treatment of NRDS generally includes positive-pressure ventilation and may include intratracheal surfactant replacement.

• Infants who are very premature (23 to 27 weeks gestation) may require positive-pressure respiratory support for several weeks. The ductus arteriosus may fail to close, leading to patent ductus arteriosus , and pulmonary edema or hemorrhage can occur. They are at increased risk for the development of chronic lung disease of infancy.

• The mortality rate from NRDS in the newborn varies by country and is dependent, in part, on the rate of premature births and the availability of appropriate treatment interventions in those who develop the disease. In the United States, the mortality rate has declined dramatically in the last several decades.

Meconium Aspiration Syndrome

• Meconium aspiration syndrome is most common in postmature infants.

• Meconium is found in the amniotic fluid in approximately 15% to 20% of all pregnancies. As a consequence, meconium aspiration as such is considered to be a relatively common event. Meconium products produce bronchial obstruction, air trapping, and a chemical pneumonitis.

• There is severe respiratory distress almost immediately , differentiating it from neonatal respiratory distress syndrome, whose onset is usually delayed by hours to a few days. However, whereas many infants with meconium aspiration have the onset of symptoms at birth, some infants have an asymptomatic period of several hours and then worsen over time.

• Clinically, there may be tachypnea, hypoxia, and hypercapnia. Small airway obstruction may produce a ball-valve effect, leading to air trapping, overdistension, and air leaks.

• Treatment is supportive, consisting of antibiotics and oxygen , inhaled nitric oxide, or extracorporeal membrane oxygenation (ECMO), if needed.

Important Points

• Imaging findings of meconium aspiration ( Fig. 27.3 ):

  • The lungs are hyperinflated with diffuse ropey densities (similar in appearance, but not in timing, to chronic lung disease of infancy).

  • There may be patchy areas of atelectasis and emphysema from air trapping.

  • Spontaneous pneumothorax and pneumomediastinum occur in 25% ( Fig. 27.4 ).

    

  • There may be an associated pneumonia , usually without air bronchograms.

  • Small pleural effusions may be present in 20%.

  

Chronic Lung Disease of Infancy (CLD)

• Chronic lung disease of infancy is a consequence of early, acute lung disease , frequently neonatal respiratory distress syndrome. CLD may also complicate meconium aspiration syndrome and neonatal pneumonia.

• It is a clinical diagnosis with recently updated definitions including a degree of oxygen dependence at certain corrected gestational ages as well as abnormal lung parenchyma on chest radiograph.

• Associated with most cases of CLD is the prior use of oxygen, which was administered under positive pressure.

• Clinically, infants with CLD have oxygen dependence, hypercapnia, and a compensatory metabolic alkalosis. They may develop pulmonary arterial hypertension and right-sided heart failure.

• CLD more often manifests in a milder form now than the severe manifestations of the disease when it was first described in 1967.

Important Points

• Imaging findings of CLD ( Fig. 27.5 ):

  • It may be impossible to distinguish early stages of chronic lung disease of infancy from later stages of NRDS.

  • The lungs are usually hyperaerated overall.

  • They may contain coarse, irregular, rope-like, linear densities representing atelectasis or, later, fibrosis.

  • These areas of atelectasis may be intermixed with lucent, cyst-like foci representing hyperexpanded areas of air trapping. Together, these processes give the lung a sponge-like appearance.

  

• Infants with CLD may require mechanical ventilation for months. Changes of CLD will revert to normal on the chest radiograph in most patients after the age of 2 years although abnormalities may still remain visible on CT of the chest.

• In any of these conditions (TTN, NRDS, meconium aspiration, and CLD), sudden worsening in the patient’s symptoms suggests the possibility of an air leak —a complication of positive-pressure ventilation in relatively noncompliant lungs. There are four manifestations of an air leak discussed in Table 27.2 , Figs. 27.6, 27.7, 27.8, and 27.9 .