The interpretation of a pediatric chest radiograph might appear challenging, but understanding the effect of technical factors and age; and a systematic approach can help us to reach a correct diagnosis.
- Check patient particulars and the side marker
- Note the projection (AP/PA)
- Note the phase of respiration
- Verify the presence of rotation
- Note the presence of artifacts, if any
- Systematic review of all the structures for abnormalities
- Suggest a diagnosis based on the radiograph and never forget to review the clinical background.
Effect of age
In a child:
- The anteroposterior diameter of the chest is usually more
- Air bronchogram frequently seen projected in the retrocardiac location in the neonate and young infant (Fig. 1.1)
- If seen more peripherally, considered pathological
- Anterior aspects of the diaphragms usually are at a higher level and the lower zones may be obscured.
Thymus
- Prominent anterior mediastinal shadow with the characteristic ‘Sail sign’ (Fig. 1.2)
- Gradually disappears at around 7–8 years of age
- Can appear very prominent in some infants and must be differentiated from a mediastinal mass or consolidation (Figs 1.3A and B)2
Figs 1.3A and B: Normal thymus mimicking anterior mediastinal mass. (A) Supine chest radiograph shows widened superior mediastinal contour, with asymmetric bulge on the right side. (B) CECT chest shows a homogeneous hypodense lesion in anterior mediastinum.
- Wavy contour (due to ribs) is helpful and sometimes a lateral projection might be of benefit
- Ultrasound shows a characteristic “starry sky appearance”.
Technical pearls
- As babies and most toddlers are imaged by an AP radiograph, do not forget about cardiac magnification
- Pleural effusion can give the appearance of increased opacity of a hemithorax, on a supine X-ray (Fig. 1.4)
- Expiratory phase (Fig. 1.5) film shows an apparent enlargement of the heart size and prominent bronchovascular markings (in a normal inspiratory film anterior end of 6th rib should be visible above the diaphragm)
- Rotation is the most common cause for unilateral increased or decreased translucency
- Skin folds may mimic pneumothorax (Figs 1.6A to C)
- On an oblique or rotated radiograph, sternal ossification centers may mimic lung nodules.
Figs 1.6A to C: (A) Skin fold mimicking left pneumothorax on a chest radiograph (arrow); (B) the child had a lipoma on the back which shows hyperintense signal on T2WI, and (C) loss of signal on T2W fat suppressed images.
Interpretation of Abnormal Radiological Signs
Radiographic abnormalities should be interpreted after consideration of the age, clinical history, examination findings, laboratory investigation and previous imaging reports, if available.
Systematic Review
Mediastinum
- Loss of visualization of the aortic knuckle indicates that the mass lies in posterior mediastinum (adjacent to the aortic arch) (Figs 1.9A to C).
- Lateral deviation of the trachea indicates a middle mediastinal mass, (e.g. bronchogenic cyst, lymph nodes).
- Posterior mediastinal mass (e.g. neurogenic tumor) may result in pressure erosion or splaying of the posterior rib ends (Figs 1.10A and B).
- Acute infection or steroid therapy may cause transient thymic atrophy. However, the possibility of an absent thymus gland must be considered (Di George syndrome) if it is persistently small.
- Rebound thymic hyperplasia and anterior mediastinal tumors may be difficult to differentiate on imaging.
Figs 1.7A and B: Mediastinal mass silhouetting the right heart border on chest radiograph (A) and axial CECT image (B) showing bulky lymph nodal mass in anterior mediastinum.
Figs 1.8A and B: Anterior mediastinal dermoid cyst. (A) Chest radiograph shows a mass obscuring the right cardiac border. (B) CECT chest axial image shows a cystic anterior mediastinal mass with peripheral rim calcification.
Figs 1.9A to C: Posterior mediastinal mass (neuroenteric cyst). CT scout image shows non-visualization of the aortic knuckle. (B) Axial CECT of chest shows a cystic lesion in posterior mediastinum. (C) Volume rendered images show vertebral segmentation anomalies in upper dorsal vertebrae.
Figs 1.10A and B: Posterior mediastinal ganglioneuroma. (A) Chest radiograph shows a large mass in posterior mediastinum causing obscuration of the margin of aortic knuckle, and splaying of the left 4th and 5th ribs, notching of the left 4th rib undersurface posteriorly (arrow). (B) CECT chest axial image shows large posterior mediastinal mass with calcification.
Heart and Great Vessels
- Normal cardiothoracic ratio is 60% in infants
- Establish situs by inspection of the bronchial anatomy, gastric bubble, the ascending and descending aorta
- Right-sided aortic arch is associated with various congenital heart diseases
- Closely inspect lungs to assess pulmonary vascularity in any case with cardiomegaly
- Visible pulmonary arterial branches in the periphery of the lung, suggests pulmonary plethora (increased blood flow)
- Non-visualization of the central pulmonary vessels suggests reduced pulmonary blood flow.
- On chest radiograph, imaging pointers of pulmonary arterial hypertension include peripheral pruning of the pulmonary arteries and enlarged central pulmonary arteries.
While abnormalities in cardiac contour may be useful to diagnose the anatomical cardiac chamber enlargement, the causes of chamber enlargement are wide and nonspecific; which requires full assessment by echocardiography.
Lungs and Pleural Cavities
Bilateral Increased Translucency (Figs 1.11A and B)
Generalized increased translucency of the thorax:
- Large inspiratory effort
- Airway diseases (asthma, bronchiolitis and cystic fibrosis)
- Upper airway obstruction due to tracheal obstruction (e.g. vascular ring or tracheal foreign body).
- Patient rotation, probably the most common cause
- Which side is abnormal
- Pulmonary vascularity
- The side with decreased vascularity is usually abnormal.
- The side with increased or normal vascularity is normal.
- Changes in appearance between inspiratory and expiratory films
- The side which shows least change on expiration is usually abnormal.
- Size of the hemithorax
- A small opaque hemithorax is usually abnormal.
- Obstructive emphysema
- Attenuated pulmonary vessels
- Expiratory film will exaggerate disparity between normal and abnormal lung
Figs 1.11A and B: (A) Chest radiograph and (B) CT lung window show generalized hyperinflation and increased translucency of the lung fields.
Figs 1.12A to C: Pulmonary hypoplasia. (A) Chest radiograph shows small hyperlucent left hemithorax, with eventration of left hemidiaphragm. (B) Axial CECT chest mediastinal window and (C) lung window reveal small left pulmonary artery and hyperlucent lung field.
- Compensatory emphysema
- Less marked on expiration
- Pulmonary hypoplasia (Figs 1.12A to C)
- Small hyperlucent lung
- Small calibre of pulmonary artery
- Swyer-James-Mcleod syndrome
- Acquired bronchiolitis obliterans
- Small lung with hyperlucency
- Air trapping and small calibre of pulmonary artery
- Chest wall causes Poland syndrome (Figs 1.13A and B).
Pneumothorax (Fig. 1.14)
- Increased translucency of the hemothorax
- Visualization of the lung margin
- Anterior loculation of the pneumothorax may be indicated by the only abnormality of increased clarity of the heart border.
Pneumomediastinum
-
Figs 1.13A and B: (A) Poland syndrome. Increased translucency of right hemithorax. (B) Axial NCCT of chest shows absent pectoralis muscles on right side.
- Increased clarity of the cardiac outline
- Air outlines the lobes of the thymus.
Increased Pulmonary Opacification
- Pulmonary infiltrates:
- Air space opacities: Air bronchograms; consolidation may be segmental or lobar in distribution (Figs 1.15A to C)
- Pulmonary edema, bronchopneumonia, aspiration changes are usually bilateral.
- Interstitial infiltrates:
- Linear pattern with peribronchial thickening—acute interstitial pulmonary edema or infection (e.g. viral bronchiolitis)
- Chronic interstitial disease—reticulonodular, nodular, miliary opacities and a honeycomb appearance (Fig. 1.16)
-
Figs 1.15A to C: Consolidation in two different patients. CT scout image (A) and CT lung window image (B) showing consolidation with air bronchogram in bacterial pneumonia. Chest radiograph (C) in another patient showing right upper lung zone consolidation with air bronchogram.Fig. 1.16: Reticulonodular shadows in a case of interstitial lung disease in Langerhan's cell histiocytosis.Fig. 1.17: Right middle and lower lobe collapse. (A) There is increased opacity of right lower lung zone with obscuration of the right cardiac border and right hemidiaphragm. Another patient with opaque right hemithorax (B) shows a metallic foreign body (C) on axial CT image.12Fig. 1.18: Complete collapse and destroyed left lung leading to increased opacity of left hemithorax.
- Pulmonary aplasia and agenesis
- Small lung volume with increased opacity
- Pleural fluid
- In supine position
- Large pulmonary/chest wall mass
- Diffuse pleural thickening.
Pulmonary Nodules
- Wide differential diagnosis
- Most common cause in childhood is ‘round pneumonia’
- Multifocal nodules are most commonly infective [septic emboli, miliary nodules (Fig. 1.19)], metastases.
- Solitary nodules can be infective (granuloma, round pneumonia), hamartoma (Fig. 1.20) or metastasis.
- Pulmonary masses (described in separate chapter 13).
Fig. 1.19: Miliary tuberculosis. Chest radiograph showing fine nodules of uniform size scattered in both the lung fields.
Ring Shadows (Figs 1.21A and B)
Ring shadows refer to air-filled cystic lesions with thin wall
- Bronchiectasis
- Cystic fibrosis
- Pneumatoceles—staphylococcal and streptococcal pneumonia
- Bronchogenic cyst
- Congenital diaphragmatic hernia
- Cystic adenomatoid malformation
- Bronchopulmonary dysplasia.
- Normal position:
- Right hemidiaphragm can normally be higher than left
- Difference of height >1.5 cm between the two hemidiaphragms abnormal
- Marked elevation:
- Loss of lung volume
- Diaphragmatic paralysis
- Eventration
- Congenital diaphragmatic hernia
- Subpulmonary effusion.
- A flattened diaphragm:
- Indicates overinflation
- Loculated subpulmonary pneumothorax.
Thoracic Skeleton and Soft Tissues
Discussed in the Chapter 9.
Figs 1.21A and B: Ring shadows in cystic bronchiectasis. (A) Chest radiograph showing ring shadows and nodules in right lower zone; (B) CT shows cystic bronchiectasis.