Category Archives: Imaging

Imaging

When To Obtain A Dedicated Facial CT

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Initial CT scan evaluation for blunt trauma patients is fairly standardized. The usual palate consists of scans of the head, cervical spine, chest, abdomen and pelvis. Some choose their “colors” individually, and others just slop everything on the canvas.

However, there are a few other scans that are occasionally helpful and/or necessary. Think soft tissue views, or CT angiogram of the neck, or CT angiogram of potential extremity vascular injuries.

Another study that is occasionally needed but many times unnecessarily ordered is the dedicated CT of the facial bones. This study spans the entire area from mandible to frontal sinus and is performed using finer cuts to display greater detail.

The unfortunate truth is that a large number of dedicated facial CTs either do not show fractures, or show fractures that don’t require operation. The scan does deliver a nice dose of radiation, though. Is there any way to be more selective about ordering it?

About 10 years ago, a plastic surgery group in Madison developed what came to be called the “Wisconsin criteria” for ordering facial imaging.  Here they are:

  • Bony step-off
  • Periorbital ecchymosis
  • GCS < 14
  • Malocclusion
  • Missing teeth

The authors claimed 97% sensitivity and 2.6% missed fracture rate, although external validation suggested those numbers were a bit generous. The Plastic Surgery group from the University of Minnesota and Regions Hospital recently re-studied these criteria with a large number of patients, looking at accuracy as well as cost-savings.

They performed a retrospective review of 1000 patients (based on a power analysis) who had a facial CT and adequate documentation of the Wisconsin criteria in the chart. Here are the factoids in table form:

(click table for larger copy)

  • Periorbital ecchymosis was the most common criterion, which had the highest sensitivity of 70% (terrible)
  • The other criteria fared even worse from a sensitivity standpoint
  • But if you roll them all up together, the presence of any one of the five yielded a 90% sensitivity (true positives) and 52% specificity (true negatives)
  • The negative predictive value was 93% if none of the criteria were present, which means it’s a good tool for ruling out the need for a CT scan
  • The overall missed fracture rate was 2.8%, and only 0.12% for ones that required operation
  • Cost savings by limiting CT to patients who met the criteria was over $300K in 2014

Bottom line: What to do? It’s clear that using the absence of any of the Wisconsin criteria to avoid a facial CT scan is helpful. This makes sense, because 4 of the 5 criteria are findings on facial exam. But it also means that a lot of scans will still get done for low sensitivity criteria. 

How about this? Since nearly all of these patients will have head and cervical CT scans, review the head scan first for facial fractures. Single, non-displaced fractures are nearly always nonoperative in nature. If patterns of fractures are present, or there are significant displacements, a dedicated facial scan will be very helpful in determining operative management.

But remember, the head CT does not include the mandible. A good physical exam and occlusion check is mandatory, and any suspicion of injury should prompt a full scan of the face.

Thanks to Chris Stewart, the lead author on this study for sending it to me for review.

Rreference: Validation of the “Wisconsin criteria” for obtaining dedicated facial imaging and its financial impact at a Level I trauma center. Craniomaxillofacial Trauma & Recon 13(1):4-8, 2020.

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General, Imaging

What? Still Using MRI For Cervical Spine Clearance?

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Cervical spine clearance as evolved considerably over the years. First, there were five views of the spine using plain radiography. Then there were three. Then we moved to CT scan with clinical clearance. And currently, many institutions are relying only on CT.

But MRI has been used as an adjunct for quite some time. Initially, it was the tie breaker in patients who had equivocal CT findings, and for a while it was used for clearance in obtunded patients. And thanks to conflicting literature and disparate studies, the occasional usage became more frequent.

The group at Cedars-Sinai Medical Center in Los Angeles  noted that the percentage of patients undergoing MRI for cervical spine evaluation at their center slowly slowly crept up from 0.9% to 5.6% over a 10 year period. They designed a study to analyze the utility of this practice and inform their future practice.

Here are the factoids:

  • Over 9,000 patients had cervical spine CT during the 10-year study period; 513 (5.6%) were positive
  • Of the 513 CT-positive patients, 290 (56%) underwent an MRI. This showed:
    • Confirmation of the major injury in 250
    • Minor injury in 40
    • Clinically significant injury was seen in only 2 which was no surprise since they both had neurologic deficits
  • Of the 8,588 CT-negative patients, only 9 had clinically significant findings and 8 of them had neurologic deficits

Bottom line: So what have we learned here? First, MRI usage at Cedars-Sinai increased over time but was really not that useful. The main use was for imaging obtunded patients or those with an obvious neurologic deficit.

More than half of patients with positive CT scans also underwent MRI. If a major injury was seen on CT, MRI confirmed it. But if the CT findings were minor, none of the MRIs added any clinically significant findings in the absence of a neurologic deficit.

And what about MRI after negative CT? In the absence of a deficit, only one had a clinically significant finding (which only required a brace).

This study shows the wisdom of monitoring “how we do it.” There is sometimes some creepage away from what the literature shows is the best practice. The best way to remedy this is to do a good study, just like the authors did. They saw a slow change in practice, investigated it, and found that there was no good clinical reason for it. This gives the trauma program the ammunition to squelch the unwelcome behavior and return the clinicians to best practices.

Reference: Is MRI becoming the new CT for cervical spine clearance? Trends in MRI utilization at a Level I trauma center. J Tra publish ahead of print, DOI: 10.1097/TA.0000000000002752, 2020.

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General, Imaging

What Are: These Spondylo… Words

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Spondylosis. Spondylolisthesis. Spondylitis. These words are tossed about blithely by our orthopedic and neurosurgical spine colleagues. But many trauma professionals are confused by the terms. What do they mean? What do they look like?

Let’s start with the root of the word, spondylo… This part is derived from the Greek word spondylos, meaning spine. Now let’s combine it with some of the usual suffixes.

The first one is -osis, so this creates the word spondylosis. Although -osis can denote the “condition of being a …”, in medicine it frequently means a disease or pathological process. Think diverticulosis of the colon. Spondylosis usually denotes a degenerative process of the spine. This is typically due to arthritis and results in bone spurs and disc narrowing. Here is an image of a spine with significant spondylosis:

Now let’s add -listhesis. This is another Greek word that means “slipping or falling.” So in this case, the full word means one vertebra slipping over another. Here’s an image of an anterior spondylolisthesis:

Finally, let’s add -itis. This is the Greek suffix for inflammation. So spondylitis is an inflammatory process of the spine. This can be due to infectious or autoimmune causes. One of the more common types is ankylosis spondylitis, which is an autoimmune variant of rheumatoid arthritis. This causes inflammation of the facet joints and the stabilizing ligaments, leading to fused vertebra and a characteristic patient posture. Here’s a rather extreme case:

I hope this little vocabulary lesson has been helpful. Now go impress your spine specialty colleagues!

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Imaging

What Is: A Pars Fracture / Defect

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Radiologists sure know their anatomy! The vast majority of the time, I actually know what they are describing. But every once in a while they’ll toss in some term that I know I probably learned about in medical school (last century). For whatever reason though, I’m just not able to retrieve it.

Which brings me to the pars fracture. Hmm. I figure that if I have to hit the books again to look something up, there are probably a few other trauma professionals out there who are dying to know what it is, too. Here’s a diagram of a typical vertebra:

The arch extending away from the vertebral body consists of the pedicles, which are connected by the lamina. A number of things jut off from this arch, including the transverse and spinous processes and the articular processes.

The area between the lamina and pedicle and adjacent to the articular process is called the pars interarticularis. This area is a bit thinner and flatter than the rest of the arch and can fracture if sufficient acute stress is applied. It can also fracture if enough chronic stress in the area occurs. This pattern is typically seen in the lumbar spine, but may also occur at the cervical level. Thus, a pars fracture or pars defect is simply a fracture through this area.

Another term you may see with regard to the pars is spondylolysis. This is defined as a defect in the pars interarticularis, typically from a fracture. So if you see either of these terms in a radiology report, recognize that they are basically one and the same.

Here is a nice image showing the location of the pars, and the axial CT appearance of “bilateral pars defects.”

Mystery solved! Amaze your friends!

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Imaging

The Cost Of Duplicate Radiographic Studies

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Speaking of radiation, here’s another tidbit. Duplicate radiographic studies are a continuing issue for trauma professionals, particularly after transfer from a smaller hospital to a trauma center. The incidence has been estimated anywhere from 25% to 60% of patients. A lot has been written about the radiation dangers, but what about cost?

A Level II trauma center reviewed their experience with duplicate studies in orthopedic transfer patients retrospectively over a one year period. They looked at the usual demographics, but also included payor, cost information, and reason for repeat imaging. Radiation dose information was also collected.

Here are the factoids:

  • 513 patients were accepted from 36 referring hospitals
  • 48% had at least one study repeated, 256 CT scans and 161 conventional imaging studies
  • Older patients and patients with low GCS were much more likely to receive repeat studies
  • There were no association with the size of the referring hospital or the ability of the patient to pay
  • Most transfers had commercial insurance; only 11% had Medicaid and 17% were uninsured
  • Additional radiation from repeat scans was 8 mSv. The average radiation dose from both hospitals was 38 mSv. This is 13 years of background radiation exposure!
  • The cost of all the repeat studies was over $96,000

Bottom line: This is an eye-opening study, particularly regarding how often repeat imaging is needed, how much additional radiation is delivered, and now, the cost. And remember that these are orthopedic patients, many of whom had isolated bony injuries. I would expect that patients with multiple and multi-system injuries would require more repeat imaging and waste even more money. It is imperative that all centers that receive transfers look at adopting some kind of electronic data transfer for imaging, be it a VPN or some cloud-based service. With the implementation of the Orange Book by the American College of Surgeons, Level I and II centers will receive a deficiency if they do not have some reliable mechanism for this.

“Level I and II facilities must have a mechanism in place to view radiographic imaging from referring hospitals within their catchment area (CD 11–42).”

Reference: Clinical and Economic Impact of Duplicated Radiographic Studies in Trauma Patients Transferred to a Regional Trauma Center. J Ortho Trauma 29(7):e214-e218, 2015.

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