Category Archives: Imaging

Radiation Exposure From Imaging At Adult vs Pediatric Trauma Centers

Anyone who reads this blog already knows I am a big believer in well-crafted and focused practice guidelines. And by focused I mean directed toward a clinical problem that typically sees a lot of variability between care providers. Use of imaging is one of these clinical problems. A surgeon may order a certain set of studies for a major blunt trauma patient, and their emergency medicine colleague might order a somewhat different set for someone with the exact same history, physical exam, and injury pattern. Who is right? Neither!

And the variability is even greater when we throw a pediatric patient into the mix. Trauma professionals tend to be even more “generous” when ordering studies on children because they are afraid they might miss something. Unfortunately, this has the potential for overuse of imaging and exposure to unnecessary radiation.

Avery Nathens and a consortium of pediatric trauma centers used the Trauma Quality Improvement Database (TQIP) to review CT imaging practices on children age < 18 over a four year period. Only blunt trauma patients were studied, and the Abbreviated Injury Scale had to be at least 2 for a minimum of one organ system. Transfer patients were excluded because there is no data on imaging for the referring hospital in the TQIP database for them. Comparisons were made between practices at adult trauma centers treating children (ATC), mixed adult/pediatric centers (MTC) and pediatric only trauma centers (PCT).

Here are the factoids:

  • Over 59,000 pediatric trauma patients were identified in the data, and about half (31,081) received at least one CT scan
  • The distribution among the three types of trauma centers was even, with roughly a third seen at each
  • Of the study group 46% had a head CT, 17% a chest CT, and 26% underwent abdominal CT
  • Injured children were more likely to undergo CT if they were older, had a higher ISS, lower motor GCS, were involved in a car crash, or had severe injuries to head or torso
  • Overall CT rates were about the same across the three types of centers (56% ATC, 57% MTC, 43% PTC)
  • Chest CT was performed 8x as much at ATC/MTC vs PTC (!)
  • Abdominal CT was performed 2x as much at ATC/MTC vs PTC
  • Lesser injured children received relatively more CT scans at ATC/MTC when compared to PTC
  • Using standard estimates of cancer risk from all CT scans received, children treated at adult or mixed trauma centers received enough radiation to cause 17 additional lifetime cancers per 100,000 patients
  • About 35 additional lifetime cancers per 100,000 would be caused by the chest and abdominal scans performed at the ATC/MTC centers when compared to pediatric-only centers

Bottom line: This is yet another reason to adopt a well-designed pediatric imaging guideline. Not only are adult centers using CT scanning much more that pediatric-only centers, but they are unnecessarily adding to the lifetime risk for cancer of our children!

As I always recommend, find a well-designed imaging guideline from an established pediatric center and “borrow” it. Sure, it may need a few minor tweaks to fit well with your hospital. That’s okay. Just get it done so your team can begin to order the initial imaging studies consistently and intelligently.

Reference: Computed tomography rates and estimated radiation-associated cancer risk among injured children treated at different trauma center types. Injury 2018, in press.  https://doi.org/10.1016/j.injury.2018.09.036

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Pan Scanning for Elderly Falls?

The last abstract for the Clinical Congress of the American College of Surgeons that I will review deals with doing a so-called “pan-scan” for ground level falls. Apparently, patients at this center have been pan-scanned for years, and they wanted to determine if it was appropriate.

This was a retrospective trauma registry review of 9 years worth of ground level falls. Patients were divided into young (18-54 years) and old (55+ years) groups. They were included in the study if they received a pan-scan.

Here are the factoids:

  • Hospital admission rates (95%) and ICU admission rates (48%) were the same for young and old
  • ISS was a little higher in the older group (9 vs 12)
  • Here are the incidence and type of injuries detected:
Young (n=328) Old (n=257)
TBI 35% 40%
C-spine 2% 2%
Blunt Cereb-vasc inj * 20% 31%
Pneumothorax 14% 15%
Abdominal injury 4% 2%
Mortality * 3% 11%

 * = statistically significant

Bottom line: There is an ongoing argument, still, regarding pan-scan vs selective scanning. The pan-scanners argue that the increased risk (much of which is delayed or intangible) is worth the extra information. This study shows that the authors did not find much difference in injury diagnosis in young vs elderly patients, with the exception of blunt cerebrovascular injury.

Most elderly patients who fall sustain injuries to the head, spine (all of it), extremities and hips. The torso is largely spared, with the exception of ribs. In my opinion, chest CT is only for identification of aortic injury, which just can’t happen from falling over. Or even down stairs. And solid organ injury is also rare in this group.

Although the future risk from radiation in an elderly patient is probably low, the risk from the IV contrast needed to see the aorta or solid organs is significant in this group. And keep in mind the dangers of screening for a low probability diagnosis. You may find something that prompts invasive and potentially more dangerous investigations of something that may never have caused a problem!

I recommend selective scanning of the head and cervical spine (if not clinically clearable), and selective conventional imaging of any other suspicious areas. If additional detail of the thoracic and/or lumbar spine are needed, specific spine CT imaging should be used without contrast.

Related posts:

Reference: Pan-scanning for ground level falls in the elderly: really? ACS Surgical Forum, trauma abstracts, 2016.

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Best of AAST #2: Cervical Spine Clearance And Distracting Injuries

Debate has forever swirled around how to clear the cervical spine. Clear clinically? CT scan plus exam? CT only? Flexion/extension views? Distracting injury?

This last one has been problematic for a long time. What is a distracting injury? Is there a difference between lower extremity wounds vs upper chest/shoulder wounds from a distraction standpoint? Is it possible to clinically clear the cervical spine if one of these injuries exist?

Finally, a multi-institutional trial was performed that strives to answer this question. Seven Level I US trauma centers participated in this 3.5 year long study. All patients with GCS > 14 underwent a standard clinical exam regardless of whether a possible distracting injury was present. Then all underwent CT evaluation of the entire cervical spine.

Here are the factoids:

  • Distracting injuries were classified into three regions: head, torso, and extremities, but no further analysis was presented in the abstract
  • Nearly 3,000 patients were enrolled and 70% had a potential distracting injury
  • A total of 233 patients (8%) had a cervical spine injury identified by CT
  • 136 patients had a cervical injury AND distracting injury, and 14 were missed by clinical exam (10%)
  • 87 patients had a cervical injury BUT NO distracting injury, and 10 were missed by clinical exam (13%)
  • Only one injury missed by clinical exam required operation

Bottom line: This study shows the usual prevalence of cervical spine injury after blunt trauma, but adds some interesting information regarding distracting injury. Basically, clinical examination will miss about 1% of patients with a negative exam, regardless of distracting injury status. Therefore, the study suggests that clinical clearance should be attempted on all patients first, regardless of “distracting injury.”

Reference: Clearing the cervical spine for patients with distracting injuries: an AAST multi-institutional trial. Session I Paper 3, AAST 2018.

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Torso Trauma CT (Nearly) ALWAYS Requires Contrast

Most stable patients with blunt trauma undergo CT scanning these days. Hopefully, it’s done thoughtfully to optimize the risk/benefit ratio using a well-designed imaging protocol. The majority of these torso imaging protocols call for the use of IV contrast. But as I’ve written before, this can pose risks, especially to the elderly and others who have some degree of renal impairment.

Unfortunately, I occasionally encounter scans done at other hospitals that omit the use of contrast. This usually hinders diagnosis significantly. And it’s usually not clear why this happened, so let’s think about it a bit.

The use of contrast in CT is designed to show blood, or things that are filled with lots of blood. Specifically, a great deal of detail about the blood vessels and solid organs is displayed.

Let’s break it down by type of scan:

  • Chest – we are really only interested in the aorta. The only way to reliably demonstrate an aortic injury is by using contrast. And this is one of those injuries that, if you miss it, the patient is very likely to die from it. Therefore, if you are ordering a chest CT properly, you must add contrast.
  • Abdomen/pelvis – generally, we are looking for solid organ injury, potential mesenteric injuries, and extravasation of blood from organs or soft tissue. Once again, the only way to really see any of these is with contrast enhancement.
  • Vascular – CT is replacing conventional angiography for the investigation of vascular injury in many cases. Obviously, this study is worthless without the contrast.

Bottom line: Pretty much any CT of the chest, blood vessels, or abdomen/pelvis must have IV contrast injected for accurate diagnosis. But what if your patient is old, or is known to have some degree of renal impairment? First, decide if you can wait until a point of care or standard creatinine measurement is done. If you can, use the result to do your own risk/benefit calculation. Is the injury you are worried about potentially life-threatening AND reasonably likely? Are there other less harmful ways to detect it? Then use them. And if you really do need the study in a patient with renal dysfunction, give the contrast, monitor the serum creatinine regularly, and do what you can to optimize and protect their renal function over the next several days.

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Are You Still Using MRI To Clear The Cervical Spine?

There is a fairly robust  amount of data that shows that, properly performed, the cervical spine can be cleared using a high quality CT read by a highly skilled radiologist. This is true even for obtunded patients. Pooled data suggest that the miss rate in this group is only 0.017%. And MRI is not perfect either, missing significant ligamentous injury in a small number of patients.

But it seems that some trauma professionals are still using MRI in some cases despite this data. The latest study on MRI focuses on the cost-effectiveness of the technique. The authors selected patients with GCS < 13 to be their obtunded group, which is probably a bit high. Nevertheless, they used a fairly sophisticated (meaning hard to understand) modeling-based decision analysis using a computerized simulation. This allowed them to compare different clearance strategies without performing large randomized clinical trials.

The authors considered MRI vs no MRI, false results, collar use and complications, MRI use with cost and complications, and the worst-case scenario of tetraplegia. Here is a flow chart of the scenarios considered. (Courtesy JAMA Surgery)

Here are the factoids:

  • The mean cost for followup vs no followup was $14K vs $1K, with no increase in quality adjusted life years (QALY)
  • No followup was the better strategy when the negative predictive value of CT was high (>98%), when the risk of an unstable injury treated with a collar turning into a permanent deficit was >25%, or if the chance of a missed injury becoming a permanent deficit was >58%
  • No followup MRI was the better strategy in all 10,000 iterations of the simulation

Bottom line: Yes, this is a fairly heavy computer simulation. But the reality is that we will never be able to design a large enough study to critically evaluate this issue and have it pass any IRB review. So it’s probably as good as it will ever get. It’s time to stop wasting money and putting obtunded patients in harm’s way by locking them into a relatively inaccessible MRI scanner for 30 minutes just to confirm the CT. Or keeping a collar until until the skin breaks down.

Here is a copy of the practice guideline we use for clearing all cervical spines, obtunded or not. Yes, there is some weirdness with soft collars, which mainly serve as a reminder to re-examine the patient at some point. But note the scan technique and requirement that it be read by a neuroradiologist for final clearance.

Related link:

Reference: Cost-effectiveness of Magnetic Resonance Imaging in Cervical
Clearance of Obtunded Blunt Trauma After a Normal
Computed Tomographic Finding

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