Category Archives: Imaging

Management Of Penetrating Neck Trauma: The Future?

In my last post, I described the evolution of the classic approach to penetrating neck injury. Today, I’ll propose a new way of managing it based on a combination of physical exam and CT scan.

This proposal is based on the high degree of accuracy that CT angiography of the neck provides. It is very sensitive for identifying even small injuries to the aerodigestive tract and vascular system. This study is based on work done at LA County – USC Hospital several years ago.

The trauma group at LAC+USC organized a prospective, multicenter study using a multidetector CT angiography of the neck for initial screening of penetrating neck injury. This allows evaluation the neck as a single unit, not as three zones. It also solves the problem of trying to apply zones to injuries that cross several of them.

The new algorithm that was tested utilized an initial physical exam, first looking specifically for “hard signs” of injury.  The following were considered the hard signs:

  • Active hemorrhage
  • Expanding or pulsatile hematoma
  • Bruit or thrill over the injured area
  • Unresponsive shock
  • Hemoptysis or hematemesis
  • Air bubbling from the wound

These patients were immediately taken to the OR and explored through an appropriate incision.

Patients with no signs or symptoms were admitted and observed for at least 24 hours. All other patients were considered to have “soft signs.” They underwent multidetector CT angiography of the neck, with a scanner having at least 40 slices. Further evaluation of these patients was based on the exam and CT scan.

Here are the factoids:

  • 453 patients with penetrating neck injury were identified during the 31 month study period
  • 9% had hard signs and were taken to OR; 50% had soft signs are underwent CT; 41% had no signs and were observed
  • For soft sign patients, 86% of scans were negative and all were true negatives after observation
  • 12% of soft sign patients had a positive scan, and of those 81% were true positives
  • 4 patients (2%) with soft signs had too much artifact for an accurate CT and other tests were performed; 1 of the 4 had an injury
  • Sensitivity of CTA was 100% and specificity was 97.5% in the soft sign patients
  • The authors concluded that CTA is very reliable for identifying injuries in patient with soft signs, and that patients with no signs do not require scanning, only observation

Bottom line: This is an intriguing paper that takes advantage of both physical examination at CT angiography. The results are impressive, but the numbers are still relatively small. It lends support to the argument that CTA is not required in all stable patients. But I can’t recommend completely changing our practice yet based on this one study. Additional numbers are certainly needed, but I suspect that this will become the norm in the future. I would also recommend that we all carefully look at our diagnostic algorithms to see other areas where we might identify and eliminate unneeded imaging, labs, etc.

Reference: Evaluation of multidetector computed tomography for
penetrating neck injury: A prospective multicenter study. J Trauma 72(3):576-584, 2012.

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IV Contrast and Trauma – Revisited

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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The Lead Gown Pull-Up: Part 2

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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The Lead Gown Pull-Up?

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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Contrast Extravasation Into The Psoas Muscle

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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