1. NEONATAL CHEST X-RAY: NORMAL FINDINGS.

Sometimes the neonatal chest radiograph may strike fear into the heart of many radiology residents, especially if we are not used to work with newborn patients and we have no knowledge of their normal chest appearance. Furthermore, radiographs in the PICU are usually performed with portable X-rays and in a single view; consequently, many of them are not technically optimal and may difficult a proper diagnosis.

First of all, we have to assess if there is good inspiration or rotation because both can mimic pathology. A chest properly inspirated usually has a trapezoidal morphology, with ribs horizontally disposed and parallel to each other, with cardiophrenic sinuses well delineated. Some authors also say that the anterior arch of the sixth rib is proyected over the diaphragm (Fig.1). Any degree of rotation may simulate disease, such as cardiomegaly or an hyperdense hemithorax (Fig.2).

Fig. 1: Characteristics of an optimal chest radiography.
References: Radiagnóstico, H.U La Fe. Valencia/ES

We should keep in mind that thymic configuration also may mimic disease and some signs are useful to identify its normal appearance (fig.3).

2. TUBES AND CATHETERS: THE IMPORTANCE OF ITS CORRECT POSITIONING.

The practice of neonatal intensive care usually requires the placement of tubes or catheters for treatment, nutrition, mechanical ventilation and to monitor blood gases and blood pressure. Some of them can be placed through an umbilical artery or umbilical vein, being the mouth the access to endotracheal and nasogastric tubes. It's essential to ensure the correct positioning of them to avoid potential complications (Fig.4):

Fig. 4: Levels of correct catheter placement.
References: Radiodiagnostico, H.U La Fe. Valencia/ES

There is disagreement about which is the correct position of the tip. Some authors suggest that the umbilical venous catheter should be placed next to the cavo-atrial junction, usually (but not always) at the level of ninth vertebral body (D9). An intracardiac placement may cause arrhythmias and even death in case of atrial wall perforation and cardiac tamponade.

Regarding umbilical arterial catheters, the level preferred is the sixth vertebral body (D6) or L3-L5, but sometimes the tip may be placed between D5 and D9. It's important to avoid the origin of main arterial vessels, whose levels are:

• D12      (level of coeliac trunk).
• D12-L1 (level of the superior mesenteric artery, SMA).
• L1-L2    (level of renal arteries).
• L3         (inferior mesenteric artery, IMA).
• L4         (aorto-iliac bifurcation).

Some newborns with respiratory distress syndrome may require an endotracheal tube which inserted via the mouth or nose into the trachea for mechanical ventilation. It should be placed 1.5 cm above the carina (with baby's head midline).

2.1 Complications associated with catheters.

Complications associated to catheters are usually related with an abnormal positioning, although sometimes are inherent to the catheter. Catheters inside an artery or into the portal vein may cause thrombosis (Fig.5) or portal cavernomatosis (Fig.6). 

Fig. 5: Complications associated with catheters: A) Incorrectly umbilical arterial catheter on a 26 weeks preterm. The tip is placed in the left subclavian artery. B) Different patient with the tip of an umbilical catheter cateter into the right portal bifurcation with consequent portal thrombosis. (C). D) Aorto-iliac thrombosis in a newborn who came from other hospital and was monitored by arterial umbilical catheter.
References: Radiodiagnostico, H.U La Fe. Valencia/ES

Hepatic perfusion defects (Fig.7) and intra-hepatic collections are also described (Fig.8).

Fig. 8: Intrahepatic collection in a preterm who underwent an incorrect umbilical catheter placement.
References: Radiagnóstico, H.U La Fe. Valencia/ES

3. MAIN CAUSES OF NEONATAL RESPIRATORY DISTRESS.

Some preterm babies may have difficulties to adapt their respiration to extrauterine life because of an incomplete pulmonary maturation. The maturation deficiency is both structural and biochemical. Structurally, a preterm lungs have an incomplete development of the alveolar system and tracheobronchial airway. 

The respiratory distress syndrome is strongly associated with the biochemical component, a surfactant deficiency, which is the most frequent cause of respiratory distress in the preterm. It is presented in the first few hours of life and symptoms include tachypnoea, expiratory grunting, nasal flaring.

Chest X-ray usually shows bilateral and symmetrical ground glass opacities or granulated pattern with diffuse distribution. Lungs are usually small and air bronchogram can be seen; These radiographic findings are usually present shortly after birth but they also may appear after 12-24 hours (Fig.9). If there is severe surfactant deficit, both hemithorax may be opaque (Fig.10). After surfactant thereapy there may be asymmetric improvement.

Fig. 9: Chest-x ray on a 27 weeks preterm shows a diffuse bilateral granulated pattern likely due to surfactant deficiency which went worse within 24 hours. After endotracheal surfactant therapy there was progressive improvement.
References: Radiagnóstico, H.U La Fe. Valencia/ES

Transient tachypnoea of the newborn (TTN), also known as retained fetal fluid, is related with neonatal tachypnoea for the first few hours of life, lasting up to one day. The tachypnea resolves by two days (Fig. 11).  This is more common in babies delivered by caesarean due to lack of thoracic compression.

Fig. 11: Difuse interstitial bilateral pattern in a newborn delivered by caesarean. This finding may be similar to surfactant deficiency but it his case is usual a rapid resolution some hours later.
References: Radiodiagnostico, H.U La Fe. Valencia/ES

Many babies with respiratory distress due to deficit surfactant (or any other etiology) may need excessive oxygen concentration and prolonged mechanical ventilation. Both therapies prolonged on time are a well known cause of bronchopulmonary dysplasia due to oxygen toxicity and barotrauma.

Initially, high levels of oxygen may cause capillary wall damage, with interstitial fluid seepage and pulmonary oedema, which allows the development of mucosal necrosis. barotrauma due to positive mechanic ventilation sometimes entails alveolar damage. Both are followed by eosinophilic exudate, squamous metaplasia  and final interstitial fibrosis.

The radiologic appearance depends on the grade of damage and fibrosis and are classified in four stages, being the third and the fourth the most serious with large lucent areas alternating with thin strands of increase opacity, an appearance that has come to be called "bubbly lungs"(Fig. 12 and Fig.13). Lungs are usually hyperinflated.

Fig. 12: 4/06/2013: Diffuse reticular pattern due to surfactant deficiency on a 24 weeks preterm who required mechanic ventilation for a long time. Endotracheal tube can be seen. 8/06/2013: Pulmonary hyperinflation and persistent reticular pattern with disperse small lucent areas. 24/7/2013: "Bubbly lungs" appearance after a month under mechanical ventilation.
References: Radiodiagnostico, H.U La Fe. Valencia/ES