Tag Archives: chest CT

Using Chest CT To Detect Occult Injuries

There are major belief systems when it comes to the use of trauma CT: selective scan vs pan scan. The selective scanners believe that too much radiation can be bad, and that the risk of excess exposure outweighs the value of scanning everything. The pan scanners believe that valuable information might be missed unless they routinely image everything.

Who is right? There’s probably value in each side of the argument. But do we have data? Good data? Two emergency medicine groups from UC-Irvine and UC-San Diego tried to answer this question via a prospective study involving 10 Level I trauma center EDs in California.  They tagged onto data collection underway for the NEXUS chest and chest CT studies from 2009-2012.

Patients with fresh (< 24 hours) blunt trauma who underwent chest imaging in the ED were included. Patients needed to have both CT scan and chest x-ray within 24 hours, at the discretion of the emergency physician. Weirdly, they skewed their sample by enrolling patients from 7am to 11pm daily due to availability of research personnel.

The researchers were looking for minor and major interventions necessitated by data discovered on the CT scan. Occult injuries were defined as clinically important if an intervention occurred because of it. Major interventions included surgery, mechanical ventilation for pulmonary contusion, or chest tube for hemo- and pneumothoraces.

Here are the factoids:

  • Nearly six thousand patients were enrolled, and 2,048 had at least one injury identified on either study
  • A total of 1,454 of these injuries (71% of injuries, but only 25% of patients) were occult, only being seen on the CT scan
  • Chest x-ray found all injuries in only 29% of patients (not surprising)
  • When pulmonary contusion was seen by CT only, 6% were placed on ventilators; when hemo- or pneumothorax were seen, 41% and 29% respectively had chest tubes inserted (wow!)
  • The authors tallied 241 major interventions for occult injury in 202 patients, 154 chest tubes for hemo/pneumothorax and/or mechanical ventilation, 9 operations for diaphragm or aortic injury, and the remainder appear to be for other chest wall fractures

The authors concluded that occult injuries were found in 71% of their patients, with the majority of those “requiring” chest tubes. They recognized some of the shortcomings in their study and stopped short of recommending a pan-scan type approach to major chest trauma.

Bottom line: This argument always boils down to diagnostic yield vs money vs radiation. Radiologists like to find as many things as they can, so CT is great. For me, it always comes back to that old saying: “if a tree falls in the woods when no one is around, does it make a sound?” 

The corollary is “if a diagnosis is found on CT that is not clinically relevant, do we care?” But wait, you say, they did have to intervene. Or did they?

Have you ever scanned a chest and seen something that makes you intubate the patient immediately and put them on a ventilator? Probably not. It’s a clinical judgement. The scan may make you a bit more wary, but you will still wait for some clinical signs that the patient needs that extra help. 

And what about chest tube insertion? I’m sure most of you have seen a modest pneumothorax on chest x-ray (1 cm away from the chest wall, extending to the 6th intercostal space, say). Ho hum. And then you get a CT scan and your eyes widen. It always looks much larger on the scan. It always does. Yet the patient is still lying there comfortably, with normal oxygen saturations. Do you really need to put a tube in? For decades, we used only the x-ray, and patients did fine.

So I don’t buy that the CT result made them do the interventions. It was the clinician’s choice based on how they interpreted the scan, not the patient’s clinical condition. Without specific guidelines that determine when interventions are indicated, it just boils down to “I do an intervention when I think the patient needs it.” And every clinician will have their own criteria and thresholds. It’s tough to learn from things done this way.

So I stick by my guns. We know that chest x-ray is flawed. But it does provide good clinical data even without a bunch of diagnostic minutiae. A good practice guideline that helps select the patients most likely to benefit from a CT scan is paramount.

As you can probably tell, I’m a selective scan kind of guy and still have not run across a study that is clean and compelling enough to make me change. And I think I’ll be waiting for a while for one of those to pop up!

Reference: Prevalence and clinical import of thoracic injury identified by chest computed tomography but not chest radiography in blunt trauma: multicenter prospective cohort study. Ann Emerg Med 66(6):589-600, 2015.

Are You Overusing Chest CT In Kids?

Many centers have developed guidelines for ordering various imaging studies, mostly in adults. These frequently dictate indications for head, cervical spine, and abdominal CT. The use of chest CT guidelines are far less common. And for the most part, such guidelines are significantly lacking for pediatric trauma evaluation.

Oregon Health Sciences University published a study detailing the use and utility of chest CT in pediatric patients, which they defined as age less than or equal to 18. They also looked at the impact of implementation of imaging guidelines for chest CT. They pooled data on blunt injuries from two Portland children’s hospitals. They collected a historical cohort over 8 years ending in 2015. One hospital had implemented region-specific imaging guidelines in 2010, and the impact of this was observed. They pooled data from both centers to identify mechanisms predictive of significant thoracic injury.

Here are the factoids:

  • Nearly 3000 patients were reviewed for thoracic CT use across the study period.
  • 1451 had chest x-ray only, 933 had chest CT only, and 567 had both
  • Although CT use in other body regions significantly declined across the study period, thoracic CT did not.
  • Chest CT changed management on only 17 of 1500 patients (1%).  There were 2 operations, 1 stent placement, 1 medical management, and 13 changes I consider rather weak (chest tube insertion, negative workup)
  • All clinically significant findings were predicted by an abnormal chest x-ray and motor vehicle mechanism

Bottom line: Chest CT continues to be overused in pediatric blunt trauma (and adults too!). This is especially unsettling due to it’s low yield and the unclear future danger of high dose radiation received during childhood. The major issue with this study is that it mixes adults and children and calls them all children. Specifically, most patients age 13-14 or above act anatomically and physiologically more like adults. It would have been nice to separate out the lower age group, but this typically results in very low numbers for analysis. In this case, it should have been possible because the median age was 13.

I recommend that all centers adopt some kind of blunt imaging guidelines to reduce clinician variability and unneeded radiation exposure. This is particularly true for children, since they are more sensitive to it and will live long enough to potentially experience the adverse effects from it. 

For both children and adults, chest CT should be reserved for evaluation of potential aortic injury, and nothing else. Rib fractures, hemothorax, and pneumothorax are best evaluated by traditional chest x-ray, and therapeutic decisions based on this alone. Abnormal chest x-ray findings, coupled with a high-energy mechanism (MVC, crush, pedestrian struck, and fall from a real height (3+ storys) should drive the decision to obtain a chest CT.

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Reference: Limiting thoracic CT: a rule for use during initial pediatric trauma evaluation. J Ped Surg, In press, Aug 28, 2017.