Case f -  Introduction to chest trauma - xray

This patient has a traumatic aortic injury.

First let us analyze the chest X-ray looking for signs of mediastinal injury.  On all trauma chest radiographs is is important to look for pneumothorax.  I windowed the xray so it is hard to look at the lungs.  There is subcutaneous emphysema and bilateral pneumothoraces which are hard to see. The patient is intubated and the ETT is OK.  There is also an NG tube well placed.

When looking at a trauma chest xray, the findings that raise suspicion for mediastinal injury are a widened mediastinum, indistinctness of the aortic contour, depression of the left mainstem bronchus, apical capping, and fractures of the first and second ribs.  This case has all of these findings except apical capping. 

Generally, the mediastinum should measure less than 8 cm on the supine AP radiograph.  A widened mediastinum suggests hemorrhage.  However, the finding is almost always secondary to technique:  trauma chest radiogrphas are lordotic, supine, AP, often with poor inspiration, and sometimes rotated.  Other more common causes of mediastinal widening include lipomatosis, tumor, and adenopathy.   A widened mediastinum is the least specific finding for aortic injury.

Indistinctness of the aortic contour suggests that there is soft tissue attenuation surrounding the aorta, i.e. hemorrhage.  In this case the aortic knob is irregular.  It should be smooth.  These arrows indicate the expected location of the lateral contour of the descending aorta but there is no interface seen.  This patient's age lends an additional clue.  You can see calcifications in the aortic arch.  This should define the boundaries of the normal aortic lumen.  However, soft tissue is seen past these markings.  In a non-traumatic setting this would suggest an aneurysm, dissection, or mass.  In the setting of trauma this suggests hemorrhage around the aortic knob.

Blood tracking into the mediastinum causes mass effect.  Blood will track into the apices resulting in apical capping.  This has the appearance of apical pleural thickening as the blood dissects between the plerua and the chest wall. This is not seen well in this case.  Blood will also track inferiorly resulting in mass effect on the left mainstem bronchus.  This bronchus usually branches in a horizontal fashion.  A mediastinal hematoma will displace the left mainstem bronchus downwards.

Fractures of the first and second ribs are associated with high energy impacts; the same type of impacts that cause aortic injury.  Additionally, ribs that are broken and displaced posteriorly can impact and directly injure the aorta.  This patient has multiple rib fractures, including displaced fractures of the left first and second ribs.

However, the most sensitive sign for aortic injury is a clinical finding: mechanism of injury.  Aortic injury is a deceleration injury.  The aorta is firmly fixed at its root, at the ligamentum arteriosum, and at the diaphragm. Rapid decelerations causes shear injury at these regions.  Most tears at the root result in death at the scene.  Tears at the diaphragm are not common.  Most people who survive to the hospital usually have injury near the ligamentum.  If the mechanism of injury is such that a competent emergency room or trauma physician believes there is a risk of aortic injury, a CT scan should be performed regardless of the radiographic findings. 

If the only abnormality on the XRAY is a widened mediastinum, the patient is stable, and the trauma team has a low suspicion for aortic injury (i.e. most elderly falls, most young people who fall down stairs or off their bike) then you should say that the abnormality is probably artifact due to technique and that an upright PA and lateral chest xray should be performed at the earliest clinical convenience.  If there is any doubt then it is not too much extra work to add a CT chest to the trauma protocol abdomen and pelvis.

Proceed to the discussion on the CT scan.