Tag Archives: aorta

What Is A Wide Mediastinum Anyway?

Trauma professionals are always on the lookout for injuries that can kill you. Thoracic aortic injury from blunt trauma is one of those injuries. Thankfully, it is uncommon, but it can certainly be deadly.

One of the screening tests used to detect aortic injury is the old-fashioned chest xray. This test is said to be about 50% sensitive, with a negative predictive value of about 80%. However, the sensitivity is probably decreasing and the negative predictive value increasing due to the rapidly increasing number of obese patients that we see.

A wide mediastinum is defined as being > 8cm in width. In this day and age of digital imaging, you will need to use the measurement tool on your workstation to figure this out.

Unfortunately, it seems like most chest xrays show wide mediastinum these days. What are the most common causes for this?

  • Technique. The standard xray technique used to reduce magnification of the anterior mediastinum (where the aortic arch lives) is a tube distance of 72 inches from the patient, shot back to front. We can’t do this for trauma patients because we can’t stand them up and are reluctant to prone them. The standard trauma room technique is 36 inches from the patient shot front to back. This serves to magnify the mediastinal image and make it look wide.
  • Obesity. The more fat in the mediastinum, the wider it looks. The more fat on the back, the further the mediastinum is from the xray plate and the greater the magnification.
  • Other mediastinal blood. Major blunt trauma to the chest can cause bleeding from small veins in the mediastinum, making it look wide.
  • Thymus. Only in kids, though.
  • Aortic injury. Last but not least. Only a few percent of people with wide mediastinum will actually have the injury.

If you encounter a wide mediastinum on chest xray in a patient with a significant mechanism for aortic injury, then they should be screened using helical CT.

Tomorrow, I’ll talk about other xray findings that can clue you in to the presence of a thoracic aortic injury. Friday, I’ll finish by discussing what the significant mechanisms are for this injury.

Thoracic Aortic Injury in Very Young Children

Trauma professionals routinely worry about the thoracic aorta when evaluating adults after major blunt trauma. The question is, how much do we have to worry about blunt thoracic aortic injury in children?

Younger children are more elastic, and their organs tend to withstand more punishment than adults. After reviewing the literature, I’ve come to the conclusion that this injury is very rare in children in the single digit age range. It’s difficult to find a good paper that addresses this question. The majority include kids up to age 16 or 18, which really skews the results. These patients are most commonly involved in motor vehicle crashes, although a significant number are also pedestrians struck by cars. 

The National Trauma Data Bank (NTDB) was queried for all children <18 years old sustaining blunt injury with at least 1 diagnosis code. There were nearly 27,000 records matching these criteria. Of these, only 34 had an injury to the thoracic aorta. And in the age range under 10, there were only 2! Both of these children were in very high energy car crashes.

The bottom line: Injury to the thoracic aorta practically never happens in children in the single digit age range. As they get closer to adolescence, they behave more like adults and become more susceptible. The diagnosis should be only be entertained in small children who are involved in very high-energy car crashes. Falls from the usual heights (2-3 stories) are probably not significant enough to cause it. A chest xray may show a full mediastinum, but this will most likely be due to a normal thymus. If investigation is warranted, the standard is to obtain a helical CT of the chest. This study would most likely be obtained anyway to evaluate the torso in a high-energy mechanism. Aortorgraphy is no longer used.

Reference: Trooskin, et al. Risk factors for blunt thoracic injury in children. J Pediatric Surg 40(1):98, 2005.