Reporting neonatal intensive care chest radiographs.

Introduction

The chest X-ray (CXR) in a neonate who is being cared for in an intensive care unit (ICU) or special care baby unit (SCBU) is performed for very specific reasons relating to the conditions affecting this age group and the management thereof. These include:

* checking the position of lines and tubes required for monitoring and treatment

* assessing complications of line and tube insertion, ventilation and hydration

* making a diagnosis when the patient presents with respiratory distress

* monitoring progression or resolution and responses to treatment action

* evaluating suspected pathology sustained during the birth

* evaluating pathology detected on prenatal imaging.

Information is part of your job

To make any sense of the CXR the radiologist must be armed with some useful information:

* Was the neonate born premature or term?

The range of disease varies, e.g. hyaline membrane disease in a premature neonate v. meconium aspiration in a term neonate.

* Was the neonate born today or some days ago?

The range of disease varies, e.g. transient tachypnoea of the newborn should resolve.

* Is this the first film or are there previous films?

This assists with development or resolution of disease and complications.

* Why is the patient being referred?

Is the CXR performed because of an acute deterioration as seen in a pneumothorax or is it performed to assess the position of a new line insertion?

* Is the patient being ventilated using positive pressure?

The patient may be on CPAP (continuous positive pressure ventilation), IPPV (intermittent positive pressure ventilation), oscillation and even ECMO (extracorporeal membrane oxygenation). (1)

Stepwise assessment

Step 1: Check line and tube positions.

Step 2: Look for a complication relating to tube or line placement.

Step 3: Look for any complication relating to ventilation or hydration.

Step 4: Look for signs of surgery, especially cardiac.

Step 5: Determine the cause of respiratory distress.

Step 6: Is there something new--progression or improvement over sequential CXRs?

Step 7: Look for any associated disease, e.g. cardiac or other anomaly.

Step 8: Is there any incidental abnormality of significance?

Step 1: Assessing line and tube positions (Figs 1 - 5)

[FIGURES 1-5 OMITTED]

If you do not do this first you will make a fool of yourself and miss the simplest diagnosis. First get used to the appearances and use of each of the commonly used tubes and lines and then evaluate their position according to an ideal. In neonates, rules of thumb are better than measurements as there are many size variations. Table I lists some of the more commonly used equipment as well as ideal positions and poor positions where appropriate.

Steps 2 and 3: Complications relating to tube and line placement and function (Figs 6 - 14)

[FIGURES 6-14 OMITTED]

Complications of intubation 

* Intubation of the right middle lobe bronchus/bronchus intermedius results in right upper lobe collapse with or without left lung collapse (Fig. 9)

* Traumatic intubation with pneumomediastinum.

Complications of ventilation

* Pneumothorax (Figs 10a - c)

* Pulmonary interstitial emphysema (Figs 11a and b)

* Pneumomediastinum

* Pneumopericardium

* Chronic lung disease (Fig. 12)

* Pitfall: Skin folds may mimick a pneumothorax but are seen to extend beyond the boundaries of the chest (Fig. 13).

Complications of a central venous line

* Fluid overload with pulmonary oedema and increased third space (soft tissue) (Figs 14a and b)

* Arrhythmia when the catheter is in the atrium.

* Thrombosis around the catheter and venous congestion of the neck.

* Incorrect passage of the catheter into a peripheral vessel.

Complications of umbilical vein catheter 

* Hepatic position may result in hepatic cystic masses.

* Positions other than the inferior vena cava or the right atrium restrict line use as a central catheter for chemotherapeutic administration and total parenteral nutrition.

Step 4: Signs of surgery

Are there features of thoracotomy, mediastinal drains, pacing wires or any surgical mediastinal clips? Identification of any features relating to cardiac surgery should trigger a radiological 'cardiac' assessment including evaluation of clips and stents, cardiac size, situs, position of aortic arch, features of pulmonary plethora and cardiac failure (Fig. 15)

[FIGURE 15 OMITTED]

Step 5: Determining the cause of the respiratory distress

The differential diagnosis of respiratory distress in a neonate can be simplified by considering whether the neonate was born term or premature (Table II). It can be further simplified by knowing the causes of increased lung density and relating them to lung volumes as well as the distribution (bilateral, symmetrical, and diffuse) of density.

Pitfalls: when the position of the ET tube is not considered (affects density), when the patient is being ventilated with positive pressure (affects lung volume), when exogenous surfactant has been administered (may change distribution), when there is superadded infection or haemorrhage (affects distribution and density), if the ductus arteriosus has remained patent (affects density) and when incidental or associated pathology has not been recognised. Remember that the most common cause of a lobar consolidation is a low ET tube or a mucus plug, (1) that the most common cause of diffusely dense lungs is underaeration /expiratory film (2-4) and that surfactant therapy via the ET tube may result in both patchy symmetrical and asymmetrical density as well as pulmonary haemorrhage. (4,5) Also a differential density between the hemithoraces is often due to rotation and may be confused with unilateral diseases such as infection or effusion (Fig. 16). (Tip: This should be assessed every time there is differential density by looking at the length of the anterior ribs visible and not by checking the medial ends of the clavicles against the spinous process as in adults.) Lastly, recognise that you may not always come to one single diagnosis and that infection, haemorrhage and oedema may co-exist with respiratory distress syndrome (RDS).

[FIGURE 16 OMITTED]

Take all findings into account and advise clinicians as to the most likely diagnosis that fits the clinical picture.

Meconium aspiration: This occurs when the foetus passes meconium, which is hyperosmolar, in utero due to hypoxaemia.

X-ray findings: Patchy but widespread collapse and consolidation with patchy air trapping. Can result in complete diffuse opacity.

Associations: Pulmonary interstitial emphysema (PIE) and pneumothorax. Susceptible to infection and secondary surfactant deficiency (Fig. 17). (1,6)

[FIGURE 17 OMITTED]

TTN (transient tachypnoea of the newborn) / wet lung: This occurs when there is impaired clearing of fluid from the lungs within 4 - 6 hours of life. It is more common after caeserian section and birth asphyxia.

X-ray findings: Bilateral increased density but predominantly from prominent vessel markings in the presence of normal or increased lung volumes.

Associations: Septal lines and effusions. Rapid recovery occurs within 12 hours but there may be reticulonodular densities at 48 - 72 hours. If there is no recovery or improvement within this time consider patent ductus arteriosus in a premature neonate or partial anomalous pulmonary venous drainage in a term neonate. (Fig. 18a and b). (1,6,7)

[FIGURE 18 OMITTED]

RDS (respiratory distress syndrome) / HMD (hyaline membrane disease): Related to surfactant deficiency, this is the most common cause of respiratory distress in a premature neonate. It results in non-closure of the ductus arteriosus due to hypoxia and raised prostaglandin E2. (3,4,8)

Findings are progressive: Ground glass density resulting from atelectasis and hyperinflation with decreased volume (unless patient is ventilated when volume may be normal or high).

Increasing density results in loss of cardiac and diaphragmatic margins first, then air bronchograms developing and then filling in of these resulting in 'white out' (Fig. 19a-e). (1,3,4)

[FIGURE 19 OMITTED]

Neonatal pneumonia: Usually due to Group B Beta haemolytic Streptococcus.

Findings: Asymmetrical lung density. May co-exist with respiratory distress syndrome (Fig. 20). (1,3,4)

[FIGURE 20 OMITTED]

Other causes of respiratory distress in a neonate: Other pathology may be diagnosed pre-natally or present acutely with respiratory distress post-natally. Table III summarises some alternatives to the differential diagnosis of respiratory distress in a neonate. Institution of appropriate therapy such as diuretic therapy for cardiac failure may lead to an improvement that helps in the diagnosis (Fig. 21).

[FIGURE 21 OMITTED]

A word on CLD (chronic lung disease) /BPD (bronchopulmonary dysplasia): This is the result of oxygen treatment and positive pressure ventilation during the first week of life for a minimum of 3 days. (1,2) The definition of this diagnosis is [O.sub.2] requirement at 36 weeks post conception age with an abnormal chest X-ray and respiratory distress. (1,2) It is the most common cause of chronic respiratory failure in children.

Findings: hyperaerated with reticular areas of fibrosis.

Associations: cardiomegaly from cor pulmonale and myocardial toxicity (Fig. 12).

Step 6: Is there improvement or deterioration?

Rapid resolution in the X-ray findings in a patient with bilateral diffuse lungs is in keeping with TTN whereas progressive changes that follow the stages of RDS probably support that diagnosis. The position of the ET tube or a vascular catheter may result in a collapsed or consolidated lung lobe and then follow-up X-ray should indicate repositioning and resolution. Sometimes follow-up X-rays after physiotherapy showing resolution of a lobar density support the diagnosis of a mucus plug rather than super-infection. Response of cardiac failure and fluid overload as well as third space fluid to diuretic therapy also helps to establish a strong diagnosis of parenchymal density on X-ray (Figs 22a and b). Deterioration of parenchymal lung changes in RDS (Figs 19a-e) with increasing ventilation requirements may result in PIE or pneumothorax which can only be detected on follow-up X-rays.

[FIGURE 22 OMITTED]

Steps 7 and 8: Are there any associated abnormalities or incidental findings?

There may also be associated anomalies or abnormalities contributing to respiratory distress or the X-ray findings. Remember that where there is one anomaly, such as a cardiac anomaly, this may be associated with oesophageal anomalies (e.g. atresia, tracheo-oesophageal fistula) which may contribute to parenchymal lung density through aspiration or infection. Chest X-ray findings may be confused in situations such as pulmonary hypoplasia where the decreased lung volume and density may be misinterpreted as collapse, or congenital lobar emphysema which may be mistaken for a pneumothorax. Situs inversus associated with congenital heart disease may be mistaken for a deviated mediastinum due to collapse. Always assess for associated anomalies and obtain a history of anything that may have been detected prenatally (Figs 23a and b). Also remember to look under the diaphragm. Necrotising enterocolitis occurs in the same premature neonates as RDS and may be noted on CXR (Fig. 24).

[FIGURES 23-24 OMITTED]

Conclusion

Have an organised method of reporting in neonatal ICU. Remember to report the lines and tubes first and to interpret any findings firstly relating to the equipment being used and then according to the suspected pathology. Keep the pitfalls in mind at all times and remember that RDS, infection, aspiration and pulmonary oedema may be indistinguishable. Lastly, listen to the ICU clinicians, because they have the 'secret' knowledge, and try to interpret the findings in relation to the clinical situation.

(1.) Gibson AT, Steiner GM. Imaging the neonatal chest. Clin Radiol 1997; 52: 172-186.

(2.) Trotter C, Carey BE. Radiology basics part II: Respiratory distress syndrome and bronchopulmonary dysplasia. Neonatal Network 2000; 19: 34-49.

(3.) Carey BE. Chest X-ray findings in respiratory distress syndrome. Neonatal Network 1994; 13(1): 67-72.

(4.) Carey BE. Chest X-ray findings in respiratory distress syndrome. Neonatal Network 2000; 19: 40-44.

(5.) Agrons GA, Harty MP. Lung disease in premature neonates: Impact of new treatments and technologies. Semin Roentgenol 1998; 23: 101-116.

(6.) Flores MT. Understanding neonatal chest X-rays Part II: Clinical and radiological manifestations of selected lung disorders. Neonatal Network 1993; 12(8): 9-15.

(7.) Carey BE, Trotter C. The chest X-ray findings in retained lung fluid. Neonatal Network 1994; 13: 65-69.

(8.) Flores MT. Understanding neonatal chest X-rays Part1: What to look for. Neonatal Network 1993; 12(7): 9-17.

S Andronikou, MB BCh, FCRad, FRCR, PhD Department of Radiology, Stellenbosch University and Tygerberg Hospital

S Soin, FRCR John Radcliffe Hospital, Oxford, UK

Table I. Ideal positions and undesirable positions for lines and
tubes on neonatal chest X-rays (1,8)

Type                                Ideal position

External
  Cutaneous [O.sub.2] and           N/A
    C[O.sub.2] monitors
  Cardiac leads                     N/A
  Thermometer                       N/A
  External part of pacing leads     N/A

Internal
  Endotracheal tube                 Medial clavicles
                                    Away from carina (1 - 1.5 cm)
                                    Head bent forward = low
                                    Head bent back = high

  Umbilical artery catheter         Above coeliac or below renal
                                      arteries
                                    Via internal iliac artery,
                                    i.e. first a downward course

  Umbilical vein catheter           Inferior vena cava above liver
                                    Direct course up via left portal
                                    and ductus venosus

  Long venous line                  Away from renal veins

  Central venous line               Superior vena cava

  Nasogastric tube                  Left hypochondrium / stomach or

  Nasojejunal tube                  jejunum respectively

  Intercostal / mediastinal drain   Intrathoracic / mediastinal

Type                                Undesirable position

External
  Cutaneous [O.sub.2] and           N/A
    C[O.sub.2] monitors

  Cardiac leads                     N/A
  Thermometer                       N/A
  External part of pacing leads     N/A

Internal
  Endotracheal tube                 High = above clavicles
                                    Low = at / below carina

  Umbilical artery catheter         High = near ductus
                                    Low = aortic bifurcation

  Umbilical vein catheter           Liver in hepatic vein
                                    Tributary vein

  Long venous line                  Near or in renal vein

  Central venous line               Atrial

  Nasogastric tube                  Oesophagus / bronchus

  Nasojejunal tube                  Looped in mouth

  Intercostal / mediastinal drain   Side holes external
                                    Subcutaneous

Table II. Causes of respiratory distress in neonates presented on
CXR (1,3,4,6,7)

Term neonate               Premature neonate         CXR findings

Meconium aspiration        Aspiration
Infection                  Infection                 Increased lung
                                                       density
Transient tachypnoea       Transient tachypnoea of   Symmetrical or
  of the newborn (TTN)/      the newborn (TTN)/        asymmetrical
Wet lung                   Wet lung
                           Respiratory distress      Focal or
                             syndrome (RDS)            diffuse
                           / hyaline membrane
                             disease (HMD)
                           Pulmonary haemorrhage
Spontaneous pneumothorax   Spontaneous               Crescentic
                             pneumothorax              lucency
                           Patent ductus /           Linear markings
                             persistent foetal       Increased
                             circulation               vascularity

Table III. Other causes of respiratory distress in a neonate (1,4)

Diagnosis

Diaphragmatic hernia                          Usually diagnosed
                                                prenatally
Pulmonary agenesis / hypoplasia
Congenital cystic adenomatoid malformation
  (CCAM) / sequestrated segment
Congenital lobar emphysema
Cardiac failure / left to right shunt /       Delayed diagnosis
  congenital heart disease
Persistent foetal circulation / patent
  ductus arteriosus (PDA)
Pulmonary oedema