Blunt injury to the thoracic aorta is one of those potentially devastating ones that you (and your patient) can’t afford to miss. Quite a bit has been written about the findings and mechanisms. But how do you put it all together and decide when to order a screening CT?
There are a number of high risk findings associated with blunt aortic injury. Recognize that they are associated with the injury, but are still not very common. They are:
- Fractures of the sternum or first rib
- Wide mediastinum
- Displacements of mediastinal structures (left mainstem down, trachea right, esophagus right)
- Loss of the aortopulmonary window
- Apical cap over the left lung
Here’s a sensible method for screening for blunt aortic injury, using CT scan:
- Reasonable mechanism (fall from greater than 20 feet, pedestrian struck, motorcycle crash, car crash at “highway speed”) PLUS any one of the high risk findings above.
- Extreme mechanism alone (e.g. car crash with closing velocity at greater than highway speed, torso crush)
Note on torso crush: I have seen three aortic injuries from torso crush in my career, one from a load of plywood falling onto the patient’s chest, one from dirt crushing someone when the trench they were digging collapsed, and one whose chest was run over by a car.
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.
This case involved a young male who had undergone a splenectomy for blunt trauma. He had an unremarkable postop course and was discharged after 5 days. He presented 2 weeks later with abdominal pain out of proportion to his exam.
The first CT scan hint showed pneumatosis of the cecum, which is decidedly unusual in a young person:
The next CT scan hint showed thrombosis in the superior mesenteric vein:
This case illustrates an uncommon yet dangerous complication of splenectomy: portal and mesenteric veinous thrombosis. It is generally believed to be caused by thrombocytosis resulting from the splenectomy. The pneumatosis is most likely due to problems resulting from venous congestion.
In this particular case, the patient’s abdominal exam was not consistent with a catastrophic problem (yet). He was taken quickly to the interventional radiography department, where a catheter was inserted and lytic therapy was begun. HIs pain resolved, and repeat CT showed recanalization of much of his portal and mesenteric venous system, as well as resolution of the pneumatosis. He was discharged on warfarin therapy.
Bottom line: Uncommon and dangerous: a bad combination. This often results in delayed diagnosis and severe abdominal complications, including loss of much of the intestine. Monitor the platelet count closely postop until it plateaus, and if it still rising on discharge from the hospital, arrange for monitoring as an outpatient. Dogma tells us to treat with aspirin or similar drugs as the count approaches 1 million/cubic mm, but good studies are lacking. Development of this particular complication requires anticoagulation, and possibly lytics or surgical resection depending on patient condition.
Hat tip to StillChucklesandNP for getting the answer with limited information, and whom I had the pleasure of meeting on a recent visit to her hospital!
Yesterday, I presented the case of a young man with abdominal pain a few weeks after a splenectomy for trauma. One slice of the CT scan was presented, which showed pneumatosis in the wall of the cecum.
There have been some great comments from readers with some interesting reasoning, especially from StillChucklesandNP. Here’s another piece of the puzzle, yet another slice from the CT scan:
- What’s this?
- Any other important information?
- What’s the diagnosis and why?
- How do you treat it?
Looking forward to more tweets and comments! Answers tomorrow.
Here’s an interesting one for you to solve!
A 20ish year old male was involved in a motor vehicle crash, sustaining a Grade IV spleen injury. He fails nonoperative management early in his hospital course, undergoing a splenectomy 6 hours later.
He has an uneventful recovery and is ready for discharge after 5 days. His platelet count has plateaued at 600K. He presents to your ED 2 weeks later complaining of abdominal pain. On exam, he is diffusely but mildly tender. His subjective complaints appear to be a bit out of proportion to his exam.
Here is one slice from his CT scan. I’ve put a nice fat arrow on it to help out. But it won’t.
- What does the scan show?
- Why is it there?
- What other key piece of information do you want to know?
- Any other studies?
- Then what?
Some hints tomorrow! Tweet your answers or leave comments below! Let’s see if anyone can figure this one out!