Neonatal Chest and Abdominal Radiographs

Neonatal chest and abdominal radiographs are supine anteroposterior (AP) films, usually taken with a portable machine through the incubator wall. They assess the lungs, heart, diaphragm, bowel gas pattern and the position of tubes and lines.

The chest film covers from the lower neck to the upper abdomen, and the abdominal film from the diaphragm to the pelvic floor.

For a newborn with possible airway, oesophageal or bowel disease, a combined chest and abdominal film ("babygram") is acceptable only to show a complete tube or catheter course. Separate collimated films are preferred.

A horizontal beam film (cross-table lateral or lateral decubitus with the affected side up) shows free air or fluid levels in a baby who cannot be placed upright. The dose is very small (about 0.02 to 0.05 mSv for a neonatal chest film). It is kept low with tight collimation, shielding of the gonads when it does not obscure anatomy, and fast detectors.

Neonatal respiratory distress affects 5 to 7% of newborns, and congenital gastrointestinal obstruction affects about 1 in 2000 births.

Radiographs distinguish the common causes of respiratory distress: respiratory distress syndrome of prematurity, transient tachypnoea of the newborn, meconium aspiration, pneumonia, pneumothorax, congenital diaphragmatic hernia and heart disease.

They also diagnose obstruction of the gut. They check that endotracheal tubes, umbilical catheters, central lines and nasogastric tubes are correctly positioned, which may be done many times in intensive care.

Indications. Respiratory distress, grunting, tachypnoea, cyanosis or apnoea. After intubation or placement of lines, tubes and drains. Suspected pneumothorax or deterioration on ventilation. Suspected congenital heart disease. Antenatally suspected diaphragmatic hernia, lung malformation or oesophageal atresia. Bilious vomiting, abdominal distension, failure to pass meconium.

Suspected necrotising enterocolitis or perforation. Feeding intolerance with signs of obstruction. Follow up of lung disease (bronchopulmonary dysplasia). Not for routine daily films without clinical change.

Contraindications and precautions. No absolute contraindication. Keep the baby warm through the incubator, with minimal handling and monitoring (heart rate, oxygen saturation). Film in a neutral position, with the arms by the sides or raised and the head midline. Fix and remove ECG leads, wires and clothing from the field where possible, because they hide lesions.

Mark the position of tube tips, and document side markers. Staff wear protection, and the machine is positioned as local rules require.

Preparation and technique. Take the chest film in inspiration if possible (crying or ventilator cycles can be timed). Centre it at the sternum with the beam at the level of the nipples.

The abdominal film is centred at the umbilicus and includes the diaphragm, the inguinal regions and the rectum. Add a lateral or decubitus view for free air.

Normal appearances. Chest: a roughly symmetrical, rounded thorax, with lungs inflated to about 8 to 9 posterior ribs (over 10 suggests hyperinflation, under 7 hypoinflation). The thymus can look large and triangular (the "sail" sign) and disappears with stress and illness. The cardiothoracic ratio is up to 0.6. The heart and aortic arch may be on the right with the stomach on the left in situs solitus.

Abdomen: gas in the stomach at birth, in the small bowel by 3 to 6 hours, and in the colon and rectum by 24 hours. The bowel loops are small and cannot reliably be separated into small and large bowel in newborns. A liver edge is visible on the right, and the abdomen is symmetrical with a mild central bowel gas pattern.

Interpretation. Check position and symmetry, lungs, heart, diaphragm, bones and tubes in turn.

• Respiratory distress syndrome (surfactant deficiency in preterm infants): low lung volumes, fine granular "ground glass" opacities, and air bronchograms reaching beyond the heart border, with a "white out" in severe disease. Surfactant treatment and ventilation change the pattern.
• Transient tachypnoea of the newborn: hyperinflation, perihilar streaky opacities, fluid in the fissures and small pleural effusions, clearing within 24 to 72 hours (in term infants after caesarean section).
• Meconium aspiration: coarse patchy opacities with hyperinflation and air trapping, with pneumothorax and pneumomediastinum as complications, in post-term infants.
• Pneumonia and sepsis: patchy or confluent opacities (group B streptococcus resembles respiratory distress syndrome) and effusions.
• Pneumothorax: a visible pleural edge with absent markings beyond it. On supine films, air collects anteriorly so that the lung appears hyperlucent with a clear heart border, a deep costophrenic sulcus, or a basal collection. A cross-table lateral or decubitus view confirms it.
• Tension pneumothorax shows mediastinal shift and a depressed diaphragm. Pneumomediastinum shows a lifted thymus ("spinnaker sail") and lucency around the heart.
• Pulmonary interstitial emphysema: cystic or linear lucencies throughout the lung in ventilated preterm infants. Bronchopulmonary dysplasia: coarse linear opacities with cystic lucencies and hyperinflation after weeks of ventilation.
• Congenital diaphragmatic hernia: bowel loops or a nasogastric tube in the chest, mediastinal shift away from the hernia, and a relatively gasless abdomen (left sided in 85%).
• Oesophageal atresia: a nasogastric tube coiled in the upper pouch (blind ending oesophagus), with gas in the stomach when there is a distal fistula (type C, 85%), and a gasless abdomen in pure atresia. Associated vertebral and cardiac anomalies are sought.
• Congenital lung malformations: congenital pulmonary airway malformation (cystic or solid mass), sequestration, lobar emphysema (hyperlucent, overinflated lobe with shift).
• Heart disease: cardiomegaly and increased or decreased pulmonary vascularity.
• Transposition of the great arteries: an "egg on a string" narrow mediastinum. Tetralogy of Fallot: a boot shaped heart with reduced flow.
• Total anomalous pulmonary venous return: a "snowman" supracardiac sign and pulmonary venous congestion. Also look for a right sided aortic arch.
• Duodenal atresia: the "double bubble" of stomach and duodenum, and no distal gas; associated with Down syndrome.
• Jejunal and ileal atresia: multiple dilated loops with air fluid levels, "triple bubble".
• Malrotation with midgut volvulus: a normal or gasless abdomen, or duodenal obstruction signs; a clinical emergency.
• Meconium ileus: dilated loops of variable size, ground glass "soap bubble" appearance, calcifications in meconium peritonitis; cystic fibrosis.
• Hirschsprung disease: distal obstruction with dilated loops and no rectal gas.
• Anorectal malformation: distended bowel and gas distance from the anal marker on an inverted or cross-table lateral film.
• Necrotising enterocolitis: dilated loops with a fixed, "unchanging" pattern, bowel wall thickening, pneumatosis intestinalis as bubbly or linear gas in the wall, and portal venous gas.
• Necrotising enterocolitis with perforation: pneumoperitoneum with a "football" sign, "Rigler" sign, or the falciform ligament sign.
• Endotracheal tube tip between T1 and T2 (2 cm from the carina in a baby with the neck in neutral position, since neck flexion moves the tube lower and extension higher).
• Umbilical venous catheter tip at the junction of the inferior vena cava and right atrium at about T8 to T9 (avoid the portal vein and liver, the right atrium and a position across the foramen ovale).
• Umbilical arterial catheter tip high at T6 to T9 or low at L3 to L4 (it descends first to the pelvis and then turns up along the aorta).
• Peripherally inserted central catheter tip at the superior vena cava or right atrial junction; nasogastric tube tip in the stomach; chest drains in the pleural space; and ECG leads and monitors as external artefacts.
• Skeleton: rib fractures (birth trauma or abuse), clavicle fractures, congenital anomalies (hemivertebrae, rib anomalies in VACTERL association), and osteopenia of prematurity.

Critical values and findings needing immediate action.

• Tension pneumothorax: immediate needle decompression and chest drain in a deteriorating baby, without waiting for the film.
• Malpositioned endotracheal tube (right main bronchus, oesophagus or too high), umbilical arterial catheter in a low lying or kinked position, umbilical venous catheter in the heart, portal vein or liver, or nasogastric tube in the airway: adjust before use.
• Pneumoperitoneum, pneumatosis with portal venous gas, or fixed dilated loop in a sick infant (necrotising enterocolitis): stop feeds, start antibiotics, nasogastric decompression and urgent surgical review.
• Bilious vomiting with any radiograph, even if normal: urgent upper gastrointestinal contrast study or ultrasound for midgut volvulus, because delay causes bowel infarction.
• Congenital diaphragmatic hernia: intubation without bag mask ventilation, nasogastric decompression and neonatal surgical referral.
• Oesophageal atresia: continuous low suction of the upper pouch, nil by mouth, and surgical referral.
• Suspected duct dependent heart disease (cyanosis with oligaemic or congested lung fields): prostaglandin infusion and urgent echocardiography.
• Rib fractures or multiple fractures in a baby: safeguarding review and skeletal survey.

Limitations and artefacts.

• Rotation and poor inspiration or expiration mimic pathology. An expiratory film appears dense with a wide mediastinum, and rotation distorts the mediastinum and lung density.
• A skin fold or the edge of an incubator mimics a pneumothorax edge (lines crossing the lung boundary and continuing beyond it). The thymus mimics a mass, consolidation or an upper lobe collapse.
• Supine films underestimate pneumothorax and effusion, and decubitus or cross-table lateral views should be added.
• Neonatal bowel loops cannot be reliably classified as small or large bowel, and a normal gas pattern does not exclude volvulus, Hirschsprung disease or other obstruction.
• Wires, tubes and ECG leads obscure details. Ventilator settings, surfactant and oxygen change the lung pattern, so films must be read with the clinical history, gestation and time since birth.
• Tube tip positions vary with the neck position, respiration and time. Daily films are not needed unless there is deterioration or the line has been adjusted.
• Radiography is limited for soft tissue, and ultrasound (head, abdomen, cardiac, lung) is used to avoid ionising radiation.
• Cumulative doses in extremely preterm infants are small but are minimised by justified imaging.

Special groups.

• Preterm infants: respiratory distress syndrome, pneumothorax, bronchopulmonary dysplasia, patent ductus arteriosus and necrotising enterocolitis are the main problems; tube position checks are frequent.
• Term infants: transient tachypnoea, meconium aspiration, pneumonia, persistent pulmonary hypertension (clear lungs with severe hypoxaemia), and congenital anomalies.
• Infants of diabetic mothers: respiratory distress syndrome, cardiomegaly, small left colon syndrome and hypertrophic cardiomyopathy.
• Infants with antenatal diagnoses: plan imaging for confirmation and surgical planning.
• Regions: neonatal sepsis and birth asphyxia drive admissions in many centres. Portable radiography and ultrasound are the main tools in neonatal units with limited access to CT or contrast studies.
• Bilious vomiting needs transfer to a paediatric surgical centre without delay.

Follow up tests. Repeat film after repositioning or adjustment of tubes and lines, cross-table lateral or decubitus film for pneumothorax and free air, echocardiography for suspected heart disease, cranial and abdominal ultrasound, upper gastrointestinal contrast study for suspected malrotation, water soluble contrast enema for meconium ileus, Hirschsprung disease and atresia,

blood gas, full blood count, C-reactive protein, blood culture, glucose and electrolytes, sweat chloride or genetic testing for cystic fibrosis, karyotype or microarray for associated anomalies, and neonatal surgical review.