Normal anatomical features on the radiograph
Due to the specific shape of the chest (the anteroposterior diameter is comparable to the transverse one), radiographs in newborns are performed predominantly in the anteroposterior view. This visually enlarges the cardiac silhouette, which is why the cardiothoracic index can normally reach up to 0.6.
The thymus has a significant impact on the radiological picture of the mediastinum:
- Its size varies greatly depending on the degree of lung expansion.
- The shadow of the gland may merge with the cardiac silhouette, widening the mediastinum.
- A wavy contour along the left border is characteristic due to impressions from the adjacent ribs.
- The classic «sail sign» (sail sign) is often identified, predominantly on the right.
- Against the background of severe prenatal or postnatal stress (e.g., severe infections, corticosteroid therapy), the thymus may undergo rapid involution.
It is important to remember artifacts: skin folds on the chest wall are often confused with pneumothorax, but upon closer inspection, they extend beyond the lateral edge of the lung. Holes in the incubator lid can project onto the lungs, mimicking a pneumatocele.
Idiopathic respiratory distress syndrome (IRDS)
Hyaline membrane disease (IRDS) affects premature infants born before 36 weeks of gestation. The main cause is a lack of pulmonary surfactant due to structural immaturity of the lungs. Normally, surfactant is synthesized by type II alveolar cells during the canalicular stage of development (16–28 weeks) and forms tubular myelin, which reduces surface tension in the alveoli.
With surfactant deficiency, the alveoli collapse, leading to hypoxia. On the radiograph, symptoms of IRDS appear rapidly, reaching a maximum by 6–24 hours of life:
- Decreased aeration of the lungs.
- Fine-granular decreased transparency — a symmetrical diffuse lesion caused by the alternation of collapsed alveoli and overexpanded bronchioles.
- Air bronchograms.
- In severe cases, the «white-out» (white-out) sign forms, caused by total atelectasis, edema, and pulmonary hemorrhage.
Respiratory support and complications
Extremely premature infants (<26 weeks) require mechanical ventilation. To prevent IRDS, corticosteroids are administered to the mother two days before delivery, and exogenous surfactant is administered to the infant via an endotracheal tube. Due to the uneven distribution of surfactant, the radiological picture may become patchy, mimicking pneumonia.
The adequacy of mechanical ventilation on the radiograph is assessed by the position of the diaphragmatic dome: ideally, it is located at the level of the 8th–10th posterior ribs.
Frequent complications of intensive care include:
- Air leaks: pneumothorax, pneumomediastinum, pulmonary interstitial emphysema (PIE).
- Patent ductus arteriosus (PDA): after surfactant therapy, pulmonary resistance drops, and the shunt changes to left-to-right. The radiograph shows cardiomegaly, pulmonary edema, and an elevated left main bronchus (due to an enlarged left atrium).
- Bronchopulmonary dysplasia (BPD): a chronic lung disease manifested on the radiograph by diffuse interstitial opacities and moderate lung hyperinflation.
Briefly: answers to topical questions
What radiological signs are characteristic of meconium aspiration syndrome?
Radiological signs of meconium aspiration syndrome are non-specific and depend on the infant's gestational age.
- In term infants (term infants) — coarse bilateral asymmetric alveolar opacities (opacification) with or without interstitial changes, bilateral hyperinflation, pleural effusion, and mild cardiomegaly.
- In premature infants (premature infants) — diffuse fine-granular opacities (fine granular opacification), similar to the picture of neonatal respiratory distress syndrome.
How does transient tachypnea of the newborn (wet lung syndrome) manifest on a radiograph?
On the radiograph, transient tachypnea of the newborn manifests as signs of fluid retention in the lungs.
- Mild hyperinflation (mild overinflation) — increased aeration of the lung tissue.
- Prominent vascular pattern (prominent blood vessels).
- Perihilar interstitial shadowing (perihilar interstitial shadowing) and interstitial opacity, most pronounced in the lower lobes.
- Fluid in the transverse fissure (transverse fissure).
- Small pleural effusions (pleural effusions).
Changes can be asymmetric with a predominance of right-sided involvement; concomitant mild cardiomegaly is possible.
What radiological stages are distinguished in the course of bronchopulmonary dysplasia (BPD)?
In the course of classical bronchopulmonary dysplasia according to Northway, four radiological stages are distinguished, which are currently rare.
- Stage I (acute injury) — air bronchogram against the background of a nodular-reticular network.
- Stage II (exudative phase) — decreased transparency of the lung fields («opacity») and blurred contours of the cardiac shadow due to edema.
- Stage III (proliferative phase) — appearance of migrating atelectases and small cystic lucencies («sponge» or «bubble» sign).
- Stage IV (fibrous-obliterative) — irreversible fibro-emphysematous changes.
The modern typical picture manifests as diffuse interstitial opacities with mild to moderate lung hyperinflation.
What congenital lung malformations can be detected on a plain chest radiograph of a newborn?
The following congenital lung malformations can be detected on a plain chest radiograph of a newborn:
- Congenital lobar overinflation (Congenital Lobar Overinflation) — an expanded hyperlucent lobe with mediastinal shift and depletion of the vascular pattern.
- Agenesis, aplasia, and hypoplasia of the lungs — diffuse opacification of one hemithorax, mediastinal shift toward the lesion, and hyperinflation of the contralateral lung.
- Congenital venolobar syndrome / scimitar syndrome (Congenital venolobar syndrome / scimitar syndrome) — the cause of asymmetric lung density without mediastinal shift.
To check chest rotation (positioning), always compare the lengths of the anterior ribs on both sides — if they are not equal, the infant is positioned obliquely.
Class and exam questions
How to distinguish a skin fold from a pneumothorax on a newborn chest X-ray?
The skin fold line can be traced beyond the lateral edge of the lung (extending outside the chest wall), whereas in pneumothorax, a clear edge of the collapsed lung is visible inside the thoracic cavity.
What causes the wavy contour of the left mediastinal border in infants?
This contour is formed by the left lobe of the normal thymus, which bears impressions from the adjacent anterior ribs.
What is the "white-out lung" sign?
This is an extreme degree of radiological manifestations of IRDS (generalized opacification) caused by massive atelectasis, edema, and fluid accumulation in immature lungs.
What else to study on this topic
- Stages of normal lung development (from embryonic to alveolar)
- Hemodynamic changes in patent ductus arteriosus (PDA) during surfactant therapy
- Radiological signs of bronchopulmonary dysplasia (BPD) and Wilson-Mikity syndrome
- Complications of positive pressure ventilation: pulmonary interstitial emphysema (PIE)
- Differential diagnosis of uneven lung aeration after surfactant administration
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