Teaching Case

Driver who suffers a traffic accident, with collision against the front car. The patient reports a strong blow to the top of the chest against the steering wheel. She was transported to the hospital. Clinically, the patient had hypoxemia, hypercarbia and increase in laboured breathing.

On chest radiograph: Although the quality of the image is not optimal, subtle interstitial-alveolar opacities are visualised in both upper lobes (Figure 1).
On CT: Geographic, non-segmental areas of ground-glass densities that do not respect the
lobar boundaries in both upper lobes. In some of them, there is subpleural sparing of 1–2 mm (Figure 2, 3 and 4). The rest of the lung parenchyma does not present pathological findings (Figure 5). There were no other significant findings related to the trauma.

Lung contusion is a focal parenchymal injury caused by disruption of the capillaries of the alveolar walls and septa, and leakage of blood into the alveolar spaces and interstitium [1]. It is the most common type of lung injury in blunt chest trauma with a reported prevalence of 17–70% [2].
They are most frequently bilateral and multiple, particularly in young patients, both in the impact and "contrecoup" areas. The main mechanism is compression and tearing of the lung parenchyma at the site of impact against osseous structures, rib fractures or pre-existing pleural adhesions [3].
The timing of the development of pulmonary contusion is often helpful in determining the
cause of areas of pulmonary opacity in trauma patients. Focal areas of pulmonary opacity appearing 24 hours or more after injury suggest diagnoses other than contusion, including aspiration, pneumonia, and fat embolism.
The accumulation of blood and edema becomes apparent at 24 h, making contusion radiographically more evident, although it is detected by CT from the initial imaging [5].

On chest radiography, pulmonary contusions feature patchy, ill-defined, coarse opacities. They do not respect anatomical segmental or lobar boundaries and usually do not present any air bronchograms. Pulmonary contusions have a
predominantly subpleural distribution. They have no gravitational distribution. On a chest X-ray sometimes contusions may not become apparent for >24 hours [4].

CT findings of contusion consist of non-segmental areas of consolidation and groundglass
opacification that predominantly involve the lung and are directed deeply into the area of trauma (more common posteriorly and in lower lobes), often sparing 1 to 2 mm of sub-pleural lung parenchyma adjacent to the injured chest wall [1, 3, 4]. CT is highly sensitive in detecting pulmonary contusions and the volume of lung involvement on CT scanning correlates with clinical outcomes [1, 2].

Patients who have pulmonary contusion are at an increased risk of developing pneumonia and respiratory distress syndrome [6].