Category Archives: Imaging

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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Best Of: Finding Rib Fractures On Chest X-Ray

A lot of people have been viewing and requesting this post recently.

Here’s a neat trick for finding hard to see rib fractures on standard chest xrays.

First, this is not for use with CT scans. Although chest CT is the “gold standard” for finding every possible rib fracture present, it should never be used for this. Rib fractures are generally diagnosed clinically, and they are managed clinically. There is little difference in the management principles of 1 vs 7 rib fractures. Pain management and pulmonary toilet are the mainstays, and having an exact count doesn’t matter. That’s why we don’t get rib detail xrays any more. We really don’t care. Would you deny these treatments in someone with focal chest wall pain and tenderness with no fractures seen on imaging studies? No. It’s still a fracture, even if you can’t see it.

So most rib fractures are identified using plain old chest xray. Sometimes they are obvious, as in the image of a flail chest below.

But sometimes, there are only a few and they are hard to distinguish, especially if the are located laterally. Have a look at this image:

There are rib fractures on the left side side on the posterolateral aspects of the 4th and 5th ribs. Unfortunately, these can get lost with all the other ribs, scapula, lung markings, etc.

Here’s the trick. Our eyes follow arches (think McDonald’s) better than all these crazy lines and curves on the standard chest xray. So tip the xray on its side and make those curves into nice arches, then let your eyes follow them naturally:

Much more obvious! In the old days, we could just manually flip the film to either side. Now you have to use the rotate buttons to properly position the digital image.

Final exam: click here to view a large digital image of a nearly normal chest xray. There is one subtle rib fracture. See if you can pick it out with this trick. You’ll have to save it so you can manipulate it with your own jpg viewer. 

Related posts:

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Part 2: Metal Splints – Can You CT Scan Through Them?

In my last post, I debunked the myth that using a pre-formed aluminum splint significantly degrades the quality of standard x-rays. But what about a study that provides much more detail, such as CT scan?

CT scan techs have told me that there would be too much artifact using any kind of metal splint. And typically, when imaging an extremity with CT, we are looking at vascular runoff. The vessels are small, and high image quality is extremely important. If the images are bad, then we risk having to give the patient another dose of both radiation and contrast.

As you know, my mantra is question everything! So i scouted around and found some images to share using one of these splints. Look closely for the intimal flap in the image below:

Can’t see it? That’s because it isn’t there! But you certainly could if it were!

Bottom line: A perforated aluminum splint causes absolutely no artifact or image degradation. Do not cause additional injury by removing it prior to imaging, either CT or conventional x-ray. Although your friendly techs, radiologists, and orthopedic surgeons may moan, it won’t hurt their ability to make decisions on the images.

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Part 1: Metal Splints – Can You X-ray Through Them?

Splinting is an important part of the trauma resuscitation process. No patient should leave your trauma resuscitation room without splinting of all major fractures. It reduces pain, bleeding, and soft tissue injury, and can keep a closed fracture from becoming an open one.

But what about imaging? Can’t the splint degrade x-rays and hamper interpretation of the fracture images? Especially those pre-formed aluminum ones with the holes in them? It’s metal, after all.

Some of my orthopedic colleagues insist that the splint be removed in the x-ray department before obtaining images. And who ends up doing it? The poor radiographic tech, who has no training in fracture immobilization and can’t provide additional pain control on their own.

But does it really make a difference? Judge for yourself. Here are some knee images with one of these splints on:

Amazingly, this thin aluminum shows up only faintly. There is minimal impact on interpretation of the tibial plateau. And on the lateral view, the splint is well posterior to bones.

On the tib-fib above, the holes are a little distracting on the AP view, but still allow for good images to be obtained.

Bottom line: In general, splints should not be removed during the imaging process for acute trauma. For most fractures, the images obtained are more than adequate to define the injury and formulate a treatment plan. If the fracture pattern is complex, it may be helpful to temporarily remove it, but this should only be done by a physician who can ensure the fracture site is handled properly. In some cases, CT scan may be more helpful and does not require splint removal. And in all cases, the splint should also be replaced immediately at the end of the study.

In my next post, I’ll look at the use of CT scans when this type of splint is in use.

 

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