Diagnosis
Distinguishing features
Choanal atresia
Nasogastric tube (NGT) cannot be placed
Congenital diaphragmatic hernia (CDH)
Loops of intestine (left) or liver (right) above the diaphragm on CXR
Cystic lesions:
Cystic lesion seen on CXR
Congenital cystic adenomatoid malformation (CCAM)
Bronchopulmonary sequestration
Congenital lobar emphysema (CLE)
Esophageal atresia +/− tracheoesophageal fistula (TEF)
Scaphoid abdomen, excessive salivation, +/− stomach bubble, +/− vomiting
Mediastinal lesions:
Diagnosed incidentally or patient develops infected cyst, secondary mass effects if large enough
Bronchogenic cysts
Mediastinal masses
Pneumothorax
Decreased breath sounds on affected side with collapsed lung on CXR
What Is the Most Likely Diagnosis?
Congenital diaphragmatic hernia (CDH). The constellation of severe respiratory distress in a full-term neonate with absent breath sounds and a scaphoid abdomen should be highly suspicious for this condition, and a chest radiograph will confirm the diagnosis (Fig. 30.1). A scaphoid abdomen describes a sunken abdominal wall with a concave, rather than the normal convex shape. It implies a smaller volume of abdominal contents than normal and may also be seen in cases of proximal bowel obstruction and malnutrition. In CDH the abdomen is scaphoid because the intra-abdominal contents have herniated into the chest.
Fig. 30.1
Chest radiograph of an infant with CDH
What Are the Most Common Causes of Neonatal Respiratory Distress?
It is important to note that the most common causes of neonatal respiratory distress are not surgical. A benign condition, transient tachypnea of the newborn accounts for more than 40 % of cases of neonatal respiratory distress. It occurs when residual pulmonary fluid remains in the lung tissue after delivery. Chest radiograph typically shows diffuse parenchymal infiltrates and a “wet silhouette” around the heart. Symptoms may last from a few hours to multiple days. In premature babies, the most common cause of respiratory distress is hyaline membrane disease or respiratory distress syndrome. This is due to a decrease in surfactant production by type II alveolar cells. Homogenous opaque infiltrates with air bronchograms are typically seen on chest radiography. Another common medical cause in term or post-term infants is meconium aspiration syndrome, and meconium-stained amniotic fluid is seen. Although less common, persistent pulmonary hypertension, pneumonia, and non-pulmonary etiologies (i.e., cardiac, renal) are also in the differential diagnosis of newborn respiratory distress.
History and Physical
What Is the Significance of the Supracostal Retractions and Grunting?
Grunting and costal retractions (subcostal, intercostal, or supracostal) indicate severe respiratory distress and should alert the clinician to impending cardiorespiratory collapse. Patients of all ages who exhibit signs of severe respiratory compromise should be intubated and placed on mechanical ventilation.
What Information Does the Pulmonary Examination Provide?
The absence of breath sounds in a newborn may be due to abnormal lung development in diagnoses such as pulmonary agenesis or bronchial atresia. Alternately, there may be a pneumothorax or a space-occupying lesion as in CCAM, CDH, teratoma, bronchopulmonary sequestration, and bronchogenic cyst.
Why Is the Heartbeat Displaced?
A displaced heartbeat occurs when a space-occupying lesion has enough volume to shift the mediastinum towards the contralateral side. Frequently a barrel-shaped chest will accompany this finding.
Why Is the Absence of Prenatal Care Important?
The majority of CDH is diagnosed prenatally by ultrasound examination or, in some cases, MRI. CDH can be successfully diagnosed as early as 15 weeks gestation; however, most are diagnosed by 24 weeks. Prenatal ultrasound findings of bowel loops seen in the thoracic cavity or shift of the heart and mediastinum towards the contralateral side are diagnostic of CDH. Therefore, the absence of prenatal care should alert the physician of the possibility of a malformation that is typically diagnosed in utero.
Pathophysiology
What Is Thought to Be the Etiology of This Condition?
Congenital diaphragmatic hernia results from failure of the septum transversum to completely divide the pleural and coelomic cavities during fetal development. Fusion of this diaphragmatic precursor is usually completed posteriorly by the 12th week of gestation. Herniation of intra-abdominal contents occurs during a critical period of lung development when the pulmonary arteries and bronchi are branching. Pulmonary hypoplasia results from decreased pulmonary mass and bronchiolar branching as well as dysfunctional surfactant production.
Are There Different Types?
Approximately 85 % of CDH occurs on the left side, 10 % on the right side, and <5 % bilaterally. The most common variant is a posterolateral defect, known as a Bochdalek hernia. Anteromedial defects, or Morgagni hernias, are much more rare and occur in a para- or retrosternal location. Although most Morgagni hernias are asymptomatic, children are more likely to present with gastrointestinal symptoms or obstruction. Diaphragmatic eventration is an even more rare condition that involves thinning of an intact diaphragm due to incomplete muscularization. Finally, diaphragmatic agenesis is the most extreme form of CDH and is characterized by complete absence of the hemidiaphragm.
What Are the Changes that Occur During Childbirth that Allow the Neonate to Transition to Breathing Air?
In utero, high pressure in the fetal pulmonary vasculature causes blood to flow away from pulmonary circulation and into systemic circulation. This is achieved through two fetal shunts. Most blood entering the right atrium is shunted through the foramen ovale into the left atrium, away from the right ventricle. Blood pumped into the pulmonary arteries from the right ventricle is shunted away from the pulmonary arterial tree into systemic circulation though the ductus arteriosus, which connects the main pulmonary artery to the aortic arch.
When a newborn takes his first breath of air, the pulmonary vascular bed transitions from a high resistance to a low resistance system causing an increase in pressure in the left atrium, relative to the right atrium. Blood flow then reverses across the foramen ovale and leads to its closure. The increase in oxygen concentration in the blood causes a local decrease in prostaglandins and subsequent closure of the ductus arteriosus.
How Is This Transition Affected by CDH?
Herniation of the abdominal contents into the thoracic cavity causes pulmonary hypoplasia on the ipsilateral side and to a lesser extent on the contralateral side. The mediastinum is shifted, thereby compressing the contralateral lung. Pulmonary hypoplasia combined with the muscular hyperplasia of the pulmonary arterial tree causes high resistance in the pulmonary arterial bed that does not reverse with the infant’s first breath. The resultant hypoxemia, acidosis, and hypotension cause pulmonary vasoconstriction, worsening the patient’s pulmonary hypertension. In summary, pulmonary hypertension results in decreased pulmonary blood flow and hypoxia and pulmonary hypoplasia results in decreased gas exchange and carbon dioxide retention.
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