Tag Archives: ct scan

General

Undergrading Spleen Injury

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We love our CT scans! They’re so high tech, with such detailed images popping up on the monitor so quickly. To take advantage of the detail, we’ve come up with fancy grading systems that can be used to direct care. But are they all they’re cracked up to be?

CT grading of spleen injury is a prime example. We’ve got a nice, detailed system that looks at laceration depth, subcapsular hematoma size and vascular injury. We can use it to predict the likelihood of needing an operation and where we should admit someone in the hospital (ICU vs ward). And when we see the injury on the screen, we believe that we can accurately apply the scoring system to these beautiful images.

But unfortunately, it’s not that simple.Scanning obtains multiple images in an axial plane and lays them out for us to look at. However, the spleen (and most other organs) and not shaped like a cube. It is curved, with complex nooks and crannies that can look like cracks. Moderate to large hematoma around the spleen can obscure lacerations. And the hilum is even more complicated and variable in shape.

Because of this, CT scans of the abdomen tend to underestimate the true extent of injury, especially in the higher grades. Grade I and II injuries are usually accurate, but in Grades III-V, the scan tends to undergrade by 1 (30% of cases) or 2 grades (45% of cases) when re-graded at surgery.

Bottom line: Grade I and II injuries are generally managed in a lower intensity setting and almost never require operation. But beware of the higher grades! It is very likely that it’s higher than you think. This means that if your patient slowly becomes tachycardic or their blood pressure softens, believe the clinical evidence. Don’t rely on a CT scan that was done hours ago that may be hiding a more severe injury than you think! (This applies to liver injuries as well)

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Reference: Correlation of operative and pathological injury grade with computed tomographic grade in the failed nonoperative management of blunt splenic trauma. Euro J Trauma Emerg Surg – Online First 2 Mar 2012.

General

Repeat Imaging: What Good Is It?

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I’ve written previously about how often imaging gets repeated once a trauma patient gets transferred to a trauma center (click here). There are many reasons, including clinical indications, need for advanced imaging (reconstructions), or lack of contrast. But at least 20% have to be repeated because the media is incompatible or not sent with the patient. Sounds like a problem, but is it a significant one?

A recent retrospective analysis of about 2,000 transfers to a Level I center looked at the reasons for repeat imaging and changes in outcome due to it. The paper found several interesting things:

  • Repeat imaging was more likely in more severely injured patients
  • Hospitals that transferred more patients to the trauma center tended to do more scans before transfer
  • Patients who had repeat imaging stayed in the ED longer waiting for definitive disposition
  • Repeat images did not improve outcomes (LOS, DC home, mortality)
  • A rough estimate of $354 more in charges was attributed to repeat imaging

Bottom line: Repeat imaging is wasteful, expensive and increases time in the ED. And don’t forget about the radiation exposure. With all the emphasis on pushing hospitals to use an electronic medical record, there needs to be a similar push to standardize methods for transferring radiographic images between hospitals to address the problem of repeat imaging.

Related posts:

Reference: Repeat imaging in trauma transfers: A retrospective analysis of computed tomography scans repeated upon arrival to a Level I trauma center. J Trauma 72(5):1255-1262, 2012.

General

IV Contrast

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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. Always think about the global needs of your patient and plan accordingly (and safely).

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

General

Identifying Bowel and Mesenteric Injury by CT

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CT scan is an invaluable tool for evaluating blunt abdominal trauma. Although it is very good at detecting solid organ injury, it is not so great with intestinal and mesenteric injuries. Older studies have suggested that CT can detect mesenteric injuries if done right, but a newly published study has shown good accuracy with a few imaging tweaks.

A Taiwanese study looked at a series of prospectively studied victims of blunt abdominal trauma. Patients with abdominal pain or a positive FAST were entrolled (total 106). IV contrast was given, and scans during the arterial, portal, and equilibrium contrast phases were performed using a multidetector scanner. Images were read in a blinded fashion.

A total of 13 of 23 patients who underwent laparotomy were found to have a bowel or mesenteric injury. Five had bowel injury, 4 had mesenteric hemorrhage, and 4 had both. Mesenteric contrast extravasation was seen in 7 patients, and this correlated with mesenteric bleeding at laparotomy.

The authors found that the following signs on CT scan indicated injury:

  • Full or partial thickness change in bowel wall appearance
  • Increased mesenteric density
  • Free fluid without solid organ injury

Bottom line: This study shows that CT scan can detect bowel and mesenteric injury reliably if you scan the patient 3 times! This seems like over-radiation and overkill. A more intelligent way to approach this would be to perform a normal trauma abdominal scan. If a suspicious area of mesenteric or bowel thickening is seen, then a limited rescan through the affected area only for equilibrium phase images may be warranted. If actual contrast extrvasation is seen, no further scanning is needed. A quick trip to the OR is in order.

Reference: Contrast-enhanced multiphasic computed tomography for identifying life-threatening mesenteric hemorrhage and transmural bowel injuries. J Trauma 71(3):543-548, 2011.

General

Pediatric CT Scans Before Transfer to a Pediatric Trauma Center

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CT scan is essential in diagnosing injury, although concerns for unnecessary radiation exposure are growing. These concerns are even greater in children, who may be more likely to have long-term effects from it. This makes avoiding duplication of CT scanning extremely important.

Unfortunately, there are only about 50 pediatric trauma centers in the US, so the majority of seriously injured children are seen at another hospital before transfer. Does CT evaluation at the first hospital increase the likelihood that a repeat scan will be needed at the trauma center, increasing radiation exposure and risk?

Rainbow Babies and Children’s Hospital in Cincinnati looked at 3 years of transfers of injured children from community hospitals. They then looked at how many of those children had an initial head and/or abdomen scan at the outside hospital, and whether a repeat scan of those areas was performed within 4 hours or arrival at Rainbow.

Numbers were small, but here are the results:

  • 33 had an outside CT scan, 28 (90%) were repeated
  • 6 had an outside abdominal scan, 2 (33%) were repeated
  • 55 did not have outside scans, none were repeated at Rainbow. (This is a weird thing to look at. I would hope that the trauma center didn’t have to repeat any of their own scans within 4 hours!)

Bottom line: It is critically important for referring hospitals to use radiation wisely! First, if the patient has obvious injuries that require transfer, don’t scan, just send. If you need to scan to decide whether you can keep the patient, use the best ALARA* technique you can. And trauma centers, please send a copy of your CT protocols to your referring hospitals so they can get the best images possible.

*ALARA = As low as reasonably achievable (applied to radiation exposure). Also known as ALARP outside of North America (as low as reasonably practicable). Click here for more info.

Related posts:

Reference: Computed tomography before transfer to a level I pediatric trauma center risks duplication with associated radiation exposure. J Pediatric Surg 43(12): 2268-2272, 2008.