Introduction
The thorax is often routinely imaged as part of a whole-body CT in adult traumas in part because it can detect life-threatening injuries and reduce mortality. However, this is not the recommended approach for imaging in children, for many reasons including the predicted injury patterns, radiation dose, and cancer risk.
Children are not just little adults
The mechanism of injury determines the pattern of injuries seen. Even with the same mechanism, injury patterns in children often differ from those seen in grown-ups.
Anatomical differences and the resulting response to thoracic trauma explain why certain injuries are more, or less, common in children. They have different body proportions than adults. The chest wall is more compliant so ribs tend to bend rather than fracture. The energy of the force is then transmitted to the underlying structures such as the lungs. This makes pulmonary contusions more common. The mediastinum and arterial structures are also more mobile and elastic meaning that aortic injuries, common in adults, are rare.
Management of thoracic trauma in children is often conservative and expectant.
Why are we so concerned about radiation?
When performing any imaging the need to identify injuries is balanced by the need to limit radiation exposure to that which is “As Low As Reasonably Achievable” (ALARA). What might be considered a safe option in adults is much less safe in children.
The growing tissues of children are more radiation-sensitive compared to mature adult tissue. Children have a longer life expectancy in which radiation damage can accumulate and the risk of cancer increases. Their smaller body size increases the amount of radiation received. Their organs are also closer together. Beams of radiation can scatter and reach adjacent organs like the thyroid and lungs.
CT scanners use a radiation dose that is significantly higher than standard chest x-rays (CXR). The risk of developing cancer from the radiation of a CT scan has been estimated to be as high as 1/500 with the risk of developing fatal cancer estimated to be as high as 1/1200.
What do the guidelines say about imaging in paediatric thoracic trauma?
NICE NG39 Major Trauma
1.5.36 “Do not routinely use whole-body CT to image children (under 16s). Use clinical judgement to limit CT to the body areas where assessment is needed.”
RCR Paediatric Trauma Protocols
The primary investigation for blunt trauma is a chest x-ray.
Penetrating trauma is an indication for contrast-enhanced CT.
Further imaging is dictated by initial radiographic findings.
The whole-body CT approach is strongly discouraged by both NICE and The Royal College of Radiologists (RCR). Both guidelines recommend that discussion with a radiologist prior to any CT should be mandatory. A review of plain films may reduce the need for further imaging.
The RCR recommend CXR as the primary investigation for blunt thoracic trauma. Any further imaging is guided by the nature of the trauma, the clinical condition of the child, and radiographic findings. When the CXR is normal and the patient conscious and clinically stable, a CT is not recommended. In penetrating trauma a contrast-enhanced CT is recommended as a first-line investigation to rule out occult vascular injury.
The RCR also have an algorithm to guide decision-making in the emergency department.
If CT is thought to be the most appropriate investigation then there should be dose-reduction protocols in place.
Other techniques such as ultrasound and MRI are also mentioned. Ultrasound is not recommended in the trauma setting due to limitations with image acquisition and operator dependency. MRI is usually reserved for acute spinal injury where the child has abnormal neurology. The need for ongoing resuscitation during MRI also limits its use in the acute setting.
How useful is a CXR?
CXR is a useful component to guide further investigation and management decisions. It can be used to detect pneumothorax, haemothorax, rib fractures, and gross mediastinal abnormalities. It’s fast and readily available. It helps early identification of life-threatening injuries and reduces the risk of decompensation during CT. It helps to identify the small number of children that require further imaging.
Rib fractures and pulmonary contusions are the most common thoracic injuries In blunt thoracic trauma in kids. Although a CT is more sensitive, these radiographically occult injuries rarely change management. Life-threatening injuries requiring emergency management, such as great vessel injuries, are exceedingly rare in children. The CXR is abnormal in the majority of great vessel injuries.
A retrospective study by Ugalde et al., of 1235 children (less than 18 years) who received both a CXR and CT chest, explored the sensitivity and specificity of CXR. This large study demonstrated a CXR sensitivity of 58% and specificity of 90% in detecting injuries. After removing lung contusions that didn’t result in a change in management, sensitivity improved to 78%. For great vessel injuries, an injury type in which diagnosis and management are crucial, the sensitivity was 23.2% and specificity 96.4%. 91% of children did not have any change in management when a CT chest was performed in addition to a CXR. Those that did had a higher Injury Severity Score. This study had the advantages of being large, conducted over a 6-year timeframe and being conducted at a combined paediatric and adult trauma centre. Although the retrospective single-centre design is a limitation, overall, the study was well conducted and analysed for the impact of demographics, injury severity, haemodynamic status, and outcome. The results support the practice of using CXR as a screening tool in the primary survey. Its high specificity implies that if negative, a CXR performs well in identifying those without disease, particularly for significant injuries such as great vessel injury.
Are we imaging appropriately?
Chest CT for children is often automatically undertaken as part of a ‘trauma series’, mirroring practice in adults. This may be due to a lack of awareness of specific guidelines for children. Concerns about admitting children for observation and effectively identifying deterioration may also feed into this.
A review of children who underwent CT scanning for trauma in England showed that they were more likely to have multiple areas scanned if they were imaged in a mixed adult and paediatric major trauma centre (MTC) rather than a stand-alone paediatric MTC. This is also reflected in data from the USA where children are more likely to have CT imaging at non-specialist centres and children with minor or moderate traumatic injuries which do not need intervention are more likely to be imaged. Little is known about the difference in imaging appropriateness between combined UK adult and paediatric MTCs and district general hospitals (DGH). Although it is assumed that the more specialist the centre the more appropriate the imaging, given the nature of trauma networks in the UK children will often present to their nearest DGH before being transferred to a combined or stand-alone paediatric MTC.
References
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Jones S, Tyson S, Young M, et al. Patterns of moderate and severe injury in children after the introduction of major trauma networks. Arch Dis Child. 2019;104(4):366-371.
Negus S, Danin J, Fisher R, et al. Paediatric trauma imaging: why do we need separate guidance?. Clin Radiol. 2014;69(12):1209-1213.
NICE. Major Trauma [NG39]. 2016. Accessible online at https://www.nice.org.uk/guidance/ng39
RCR. Paediatric Trauma Protocols. 2014. Accessible online at https://www.rcr.ac.uk/publication/paediatric-trauma-protocols
Strait L, Sussman R, Ata A, Edwards MJ. Utilization of CT imaging in minor pediatric head, thoracic, and abdominal trauma in the United States. J Pediatr Surg. 2020;55(9):1766-1772.
