Chest radiograph interpretation in children — formative SAQs

SAQ 1 (10 marks)

A 3-year-old is brought to the emergency department with a 2-day history of fever and cough. A chest radiograph is performed in the department as an erect PA film. You are the paediatric registrar asked to interpret the film systematically before the formal radiologist's report is available. [1] [3]

1. Outline the structured technical-quality check you will perform before reading the lung fields, naming the five components and the finding that indicates adequacy in each. (5) [1] [3]
2. Describe the ABCDEFGH systematic review, stating what you look for in each zone. (3) [1]
3. State the named radiographic sign that localises an alveolar opacity to a particular lobe by the border it erases, and the sign that confirms the opacity is alveolar rather than pleural. (2) [1]

Model answer — SAQ 1

(1) Technical-quality check (5). I assess five components before reading the fields. First, projection: I confirm the film is PA, AP, or lateral, and that the projection matches the clinical question; a PA film in a cooperative child is the reference standard because the heart is least magnified. Second, position: erect or supine — an erect film best shows the apices, the costophrenic angles, and a small pleural effusion that layers dependently. Third, rotation: I check that the medial ends of the clavicles are symmetric and equidistant from the spinous processes; if they are not, the child is rotated and the heart and mediastinum are unreliable, because rotation widens the mediastinum and magnifies the heart. Fourth, inspiration: I confirm that at least nine posterior ribs cross the diaphragm at the midclavicular line; fewer indicates under-inflation, which crowds the ribs, elevates the diaphragm, and falsely enlarges the heart. Fifth, penetration: I confirm that the thoracic spine is just visible through the cardiac shadow and the intervertebral discs of the lower thoracic spine are seen; if the film is too white the mediastinal detail is lost, and if too black the lung detail is burned out. If the film fails any of these, I flag it as limited and interpret the key findings with the limitation stated. [3] [1]

(2) ABCDEFGH review (3). I review the film zone by zone. A — Airway: the trachea should be midline and the carina visible; deviation suggests a tension process, a mass, or volume loss. B — Bones: I trace every rib, the clavicles, and the spine for fractures or lytic or sclerotic lesions; in suspected non-accidental injury I look specifically for posterior rib fractures near the costovertebral junctions. C — Cardiac: the heart size and shape, the cardiothoracic ratio on a good film, and the silhouette sign to localise adjacent consolidation. D — Diaphragm: both hemidiaphragms should be sharp, the right slightly higher than the left, and the costophrenic angles clear. E — Effusions: I look in the dependent spaces and behind the heart, remembering a supine film hides free fluid. F — Fields: I assess the lung zones for aeration, consolidation, nodules, interstitial change, and air-trapping, comparing side with side. G — Gastric and gadgets: I identify every tube and line and confirm its position. H — Hilum and mediastinum: the hila should be symmetric with the left slightly higher, the mediastinal contour is traced, and the thymus is recognised as normal in the young child. [1]

(3) Named signs (2). The silhouette sign localises disease to a lobe by the border it erases: an opacity that obliterates the right heart border lies in the right middle lobe, and one that obliterates the diaphragm lies in the lower lobe, because a pathological density of soft-tissue attenuation adjacent to a structure of similar density destroys that structure's normal border. The air bronchogram — dark branching bronchi seen against the white background of consolidated alveoli — confirms that the opacity is alveolar and within the lung, rather than pleural or chest-wall in origin. [1]

SAQ 2 (10 marks)

A term neonate born by emergency caesarean section develops respiratory distress in the first hour of life and is intubated in the neonatal unit. A chest radiograph is performed to characterise the lung disease and to check the positions of the endotracheal tube and the umbilical venous catheter. [4] [5]

1. Describe the radiographic features of neonatal respiratory distress syndrome and explain how it is distinguished from transient tachypnoea of the newborn on the chest film. (4) [4]
2. State the correct position of the endotracheal tube tip and the umbilical venous catheter tip on the neonatal chest film, and explain why the endotracheal tube position is dynamic. (4) [4]
3. Explain the radiation-aware principle of justification and ALARA as it applies to the neonatal chest film, including why children are more radiosensitive than adults per unit dose. (2) [4]

Model answer — SAQ 2

(1) RDS versus TTN (4). Neonatal respiratory distress syndrome (surfactant deficiency) shows a symmetric, fine reticulogranular pattern with low lung volumes and air bronchograms, reflecting diffuse alveolar collapse from surfactant deficiency; it is most common in the preterm infant but can occur in the term infant. Transient tachypnoea of the newborn, by contrast, shows good lung volumes with streaky perihilar densities, fluid in the fissures, and sometimes a small pleural effusion, reflecting retained fetal lung fluid that resolves over the first 24 to 72 hours. The discriminator on the film is the lung volume: low with reticulogranular change in RDS, good with perihilar streakiness and fluid in the fissures in TTN. [4]

(2) Tube and line positions (4). The endotracheal tube tip should lie midway between the clavicles and the carina, ideally at the level of the interclavicular line. The position is dynamic because flexion and extension of the neck move the tip by several centimetres relative to the carina: a tube that looks adequate in flexion may slip into the right main bronchus in extension, over-expanding the right lung and collapsing the left, while a tube near the clavicles in extension may sit above the cords in flexion. The umbilical venous catheter should run through the umbilical vein, the portal vein, and the ductus venosus to lie in the inferior vena cava at the level of the diaphragm, just below the right atrium; a catheter that stops in the portal venous system risks portal vein thrombosis and ineffective delivery. The umbilical arterial catheter, if present, should sit high (T6 to T10) or low (L3 to L5), avoiding the origin of the renal and mesenteric arteries. [4]

(3) Justification and ALARA (2). The neonatal chest radiograph is a low-dose investigation with an effective dose of roughly 0.02 mSv, equivalent to a few days of natural background radiation, and the lifetime attributable cancer risk from a single film is extremely low. The principle is nonetheless one of justification and ALARA (as low as reasonably achievable): the film is requested only when it will change management, and the dose-reduction features of modern digital radiography are used. Children are more radiosensitive than adults per unit dose because of their longer remaining life expectancy (more time for a radiation-induced cancer to manifest) and the higher proportion of actively dividing cells, which is the biological basis for the ALARA principle in paediatrics and for substituting ultrasound and MRI where they answer the question. [4]