Category Archives: Imaging

Imaging

IV Contrast and Trauma – Revisited

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We use CT scanning in trauma care so much that we tend to take it (and its safety) for granted. I’ve written quite a bit about thoughtful use of radiographic studies to achieve a reasonable patient exposure to xrays. But another thing to think about is the use of IV contrast.

IV contrast is a hyperosmolar solution that contains some substance (usually an iodine compound) that is radiopaque to some degree. It has been shown to have a significant impact on short-term kidney function and in some cases can cause renal failure.

Here are some facts you need to know:

  • Contrast nephrotoxicity is defined as a 25% increase in serum creatinine, usually within the first 3 days after administration
  • There is usually normal urine output and minimal to no proteinuria
  • In most cases, renal function returns to normal after 3-4 days
  • Nephrotoxicity almost never occurs in people with normal baseline kidney function
  • Large or repeated doses given within 72 hours greatly increase risk for toxicity
  • Old age and pre-existing diabetic renal impairment also greatly increase risk

If you must give contrast to a patient who is at risk, make sure they are volume expanded (tough in trauma patients), or consider giving acetylcysteine or using isosmolar contrast (controversial, may still cause toxicity).

Bottom line: If you are considering contrast CT, try to get a history to see if the patient is at risk for nephrotoxicity. Also consider all of the studies that will be needed and try to consolidate your contrast dosing. For example, you can get CT chest/abdomen/pelvis and CT angio of the neck with one contrast bolus. Consider low dose contrast injection if the patient needs formal angiographic studies in the IR suite. And finally, consider what changes will be made if the study is positive. For example, if a CT angio of the neck for blunt carotid/vertebral injury is being considered, the intervention for a positive result is usually just aspirin. Since this is a very benign medication, why not forgo the scan and just start aspirin if there is a significant risk of kidney injury from the contrast. Always think about the global needs of your patient and plan accordingly (and safely).

Reference: Contrast media and the kidney. British J Radiol 76:513-518, 2003.

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Imaging

The Lead Gown Pull-Up: Part 2

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Okay, so you’ve seen “other people” wearing perfectly good lead aprons lifting them up to their chin during portable x-rays in the trauma bay. Is that really necessary, or is it just an urban legend?

After hitting the medical radiation physics books (really light reading, I must say), I’ve finally got an answer. Let’s say that the xray is taken in the “usual fashion”:

  • Tube is approximately 5 feet above the xray plate
  • Typical chest settings of 85kVp, 2mAs, 3mm Al filtration
  • Xray plate is 35x43cm

The calculated exposure to the patient is 52 microGrays. Most of the radiation goes through the patient onto the plate. A very small amount reflects off their bones and the table itself. This is the scatter we worry about.

So let’s assume that the closest person to the patient is 3 feet away. Remember that radiation intensity diminishes as the square of the distance. So if the distance doubles, the intensity decreases to one fourth. By calculating the intensity of the small amount of scatter at 3 feet from the patient, we come up with a whopping 0.2 microGrays. Since most people are even further away, the dose is much, much less for them.

Let’s put it perspective now. The background radiation we are exposed to every day (from cosmic rays, brick buildings, etc) amounts to about 2400 microGrays per year. So 0.2 microGrays from chest x-ray scatter is less than the radiation we are exposed to naturally every hour!

The bottom line: unless you need to work out you shoulders and pecs, you probably don’t bother to lift your lead apron every time the portable x-ray unit beeps. It’s a waste of time and effort! Just stand back and enjoy!

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Imaging

The Lead Gown Pull-Up?

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Trauma Team members typically wear a lead gown under their personal protective equipment so they don’t have to run out of the room when x-rays are taken. How often do you see people do this?

Is it really necessary? Or is it just a way to exercise your pecs and biceps? Tomorrow I’ll talk about how much radiation team members are really exposed to so you can decide if this is really necessary.

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Imaging

Contrast Extravasation Into The Psoas Muscle

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Contrast extravasation after major trauma can be very problematic. Extravasation into a solid organ (liver, spleen) generally requires a quick trip to interventional radiology or the operating room. Bleeding from the bowel mesentery assures an exploratory laparotomy. Gluteal vessel extravasation is best treated with angioembolization.

But what about extravasation from off the beaten path areas like the psoas muscle? This is an uncommon finding on trauma CT, so less is known about the usual clinical course. A group in Okayama Japan performed a 10-year retrospective review of data from their hospital. They reviewed hematoma size, associated injuries, and the relationship to treatment options.

Here are the factoids:

  • 762 contrast CTs were performed due to blunt trauma over the 10 year period (only 76 per year?!)
  • About 15% (117 patients) had either lumbar process fracture or psoas hematoma, and about one quarter had obvious contrast extravasation into the muscle
  • Patients with contrast extravasation were significantly older, had higher ISS, and were more likely to require transfusion
  • There was an association between the number of transverse process fractures and “need for” angioembolization
  • Size of the psoas hematoma was predictive of the need for angioembolization
  • Angioembolization of the psoas was frequently associated with  embolization of the pelvis

The right psoas has both contrast extravasation and a sizable hematoma

Bottom line: This study has many weaknesses, but does show that psoas extravasation occurs somewhat frequently, even at a low volume center. I always worry about studies that state something like “and xx patients required intervention.” Generally, this means that it was performed at the discretion of the clinician and no consistent rules were applied. And even though hematoma size was significantly correlated with angioembolization, it’s probably not worth the effort to have your radiologist calculate it. But it does illustrate one nearly universal trauma rule:

Patients with active extravasation on CT are bleeding to death until proven otherwise

Do not sit back and manage expectantly! The corollary to this rule is:

Contrast extravasation on CT always requires active measures to stop it

These active measures are typically angioembolization for difficult to reach areas in hemodynamically stable patients (gluteal artery for buttock, lumbar artery for psoas muscle, solid organs). Unstable patients absolutely require a trip to the OR for control. Superficial muscular bleeding frequently stops with good pressure dressings or positioning the patient so they lie on the affected area. Just don’t sit around and watch these patients bleed when you see extravasation on the CT.

Reference: Impact of contrast extravasation on computed tomography of thepsoas major muscle in patients with blunt torso trauma. J Trauma 86(2):268-273, 2019.

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Abstracts, Imaging

EAST 2019 #10: Incidental Findings In Trauma Imaging

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Every major trauma patient undergoes some type of radiographic imaging during their initial evaluation. On occasion, some incidental finding unrelated to trauma shows up unexpectedly. These incidentalomas add several additional layers of complexity to the evaluation process.

What does the finding mean? Is it important? How do I tell the patient? Their primary care provider? When? Many times, these findings have little clinical significance. But on occasion, they can be life changing, such as the incidental renal cell carcinoma.

The group at University of Tennessee – Knoxville reviewed one year of incidental findings in trauma evaluations at their Level I trauma center. They specifically looked at diagnoses with malignant potential, and how findings were disclosed to the patient.

Here are the factoids:

  • Over 6000 patients were reviewed, and 22% had 1222 incidental findings (that’s 2 per patient!)
  • The findings were noted in males about 2/3 of the time
  • 59% of of incidentalomas were in the chest, and 16% in the abdomen
  • The most common findings were lung nodule (209), hernia (112), and renal cyst (103)
  • Only 60% of patients were informed prior to discharge (!)
  • Trauma registry abstraction resulted in an additional 20% of patients informed of the finding
  • 58 patients could not be located, and in 43 patients there was no documented attempt to contact them
  • An additional 100 registry charts that did not contain incidental findings were re-abstracted and searched for incidental findings. Nearly one third contained incidental findings!
  • If the incidental finding was noted in the radiology report summary, 78% of patients were informed. But when it was buried in the body of the report, only 22% were disclosed.

Here are some questions for the authors and presenter to consider in advance to help them prepare for audience questions:

  • The majority of the incidental findings were in the chest and abdomen. What and where were the rest?
  • What would you recommend for achieving optimal disclosure based on your results? It appears that 20% or so of patients never learned of the finding.
  • What should we do about our registry data? Should we force our registrars to comb all reports for possible incidental findings? Given that one fifth of patients have them (or more) that seems like a lot of work!
  • How has your work changed your practice at UT Knoxville?

This is a fascinating paper, and gives me some ideas for upcoming blog posts! I will definitely be in the audience for this presentation.

Reference:  A novel use of the trauma registry: incidental findings in the trauma patient. EAST 2019, Quick Shot Paper #13.

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