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After evaluating this article, participants will be able to:
1. Understand the applications and limitations of contrast with respect to CT
2. Incorporate evidence-based strategies for imaging into current practice
3. Make appropriate choices for diagnostic imaging, resulting in improved throughput and patient safety
Opener: Don’t Rush Non Contrast
Consider the Three Rs
by Jeannette Wolfe, MD
It’s a bustling Saturday night and the patient in room 4 looks like a hot appy. As she near syncopized when you suggested rectal contrast, you’re now contemplating a non-contrasted CT scan (NCC) versus a long drink oral contrast scan (OCC). That NCC is mighty tempting. It would get her to the OR before the surgeon hits REM sleep and the bars close, and there is even that recent Annals meta-analysis that suggests its sensitivity is about 93% for appendicitis (Hlibczuk V, Annals EM, 2010). But before you double click that order, consider the R cubed factor- the radiologist, the radiation and the rescan.
How comfortable are your radiologists really in interpreting NCCs for acute abdominal complaints other than renal stones and triple A?
There are a few institutions that have published high sensitivity and accuracy NCC rates but these numbers don’t always generalize to other settings. For example, Hershko (Dis Colon Rectum 2007) recently noted an overall accuracy of just 70% in their NCCs for appendicitis.
We studied this NCC/OCC question a few years ago at our hospital. We had published a dismal 10-hour median time until disposition in our ED patients getting routine OCCs (Huyhn L, Emergency Radiology 2004) and were very intrigued about the potential of using NCC scans. So we examined 100 ER patients getting non traumatic abdominal CT’s for acute abdominal pain and scanned them both without and with oral contrast with a different radiologist interpreting each scan (Lee S, Emergency Radiology, 2006). Yes, we realize that this would never get through an American IRB in 2010. Unfortunately, we found that the interpretations of the NCC and OCC scans were in disagreement 21% of the time. We even ran a planned subset analysis of patients with a higher BMI- anticipating that increased intraperitoneal fat would highlight pathology (Wolfe J, Amer J Emerg Med 2006). Again, big zilcho- the scans were simply interpreted differently. In post-hoc analysis we reasoned that much of these differences were probably due to inter reader variability, or simply stated, perhaps it wasn’t the contrast that mattered but how Bob read CTs differently than Steve. So we mixed up all of the discordantly-read scans and asked two of our radiologists to reinterpret them. One read the OCC and NCC films similarly 98% of the time, the other did so 88%. Not terrible if the rest of our group fell between these numbers. We didn’t study that, but we did ask our radiologists how confident they would have been in interpreting the NCC as the definitive study. 45% of the time they would have requested additional imaging.
Now much of the comfort with NCCs may be institutional culture or an initial NCC learning curve, but some radiologists really feel passionate about the additional benefits of bowel/cecal opacification in delineating pathology, especially in thin patients. If these guys are not on board and you are ordering a lot of NCCs, you are going to get a lot of “equivocal” readings.
Here are some concerning stats: 8% of all ED patients get an abdominal CT scan (Broder Radiology 2006) and 10% of renal colic patients have had five scans or more (Broder J Emerg Med 2007). So what are the real risks of radiation? It is widely accepted that there is no completely safe radiation dose and that risks increase after 10 milli-sieverts (mSv). Risks are assessed by the age and sex of the patient, the “effective dose” of radiation to an exposed organ and the sensitivity of that organ to develop a radiation induced cancer. Risks are also cumulative over time. There are two recent studies that should give every EP and radiologist night sweats. Berrington de Gonzalez (Arch Intern Med 2009) estimated that of the 70 million CT scans done in America in 2007, 27,000 will cause radiation-induced cancers – 14,000 of them from abdominal pelvic CTs. Similarly, Smith-Bindman (Arch Internal Medicine 2009), looked at the effective dose of radiation of CT studies at four different California hospitals. She found great variability in radiation doses both within and between hospitals for the same type of CT study. Most concerning at one hospital was that the median dose for an abdominal-pelvic CT scan was 43 mSv – four times the commonly quoted dose! Yikes!
As a specialty we need to be more judicious about CTs. Let’s start by decreasing CTs (along with ED length of stay) in men with classic signs of appendicitis. Statistically, they have it more than 90% of the time – they need a surgeon, not a CT. If your surgical colleagues have forgotten this, here are two great papers to share: Coursey C, Radiology 2010; Antevil J, J AM Coll Surg. 2006.
Likewise, we under-utilize ultrasound (US). Lee (AJR 2005) published an astounding 98% visualization of the appendix on US after using a few simple maneuvers that reposition the appendix. OK, in most hands, US isn’t that perfect. But if you see an abnormal appendix, you are done, so consider it in patients who are not morbidly obese. They can always be sipping their backup oral contrast while they wait. And don’t forget about US for renal colic. As most stones are less than 5mm and will spontaneously pass, hematuria and an ultrasonographic normal aorta with hydronephrosis is all you really need most of the time. Finally, consider developing protocols for appendicitis and stones that use area focused scanning or lower radiation doses to decrease patient risks.
“Equivocal” scans are the bane of an EP’s existence. As Daly (AJR 2005) showed that up to 30% of patients with an equivocal RLQ scan still had appendicitis, these scans leave us in dispo purgatory. We are essentially left with: sending the patient home- hoping they can and will actually follow precautions; getting a wishy-washy consult; or rescanning. I believe that NCC’s increase equivocal reads and the risk of rescanning. In Hershko’s NCC study (Dis Colon Rectum 2007) 20% of the scans were equivocal, and in Tamburrini’s study (Eur Radiol 2007) they had a 23% rescan rate! Ironically, this study was the poster child in the Annals meta-analysis supporting NCCs. A rescan should be the exception not an accepted double-digit policy.
My bottom line: NCCs are not ready for prime time and should be reserved for patients who can’t tolerate enteric contrast or have acute peritonitis.
Read the Counter: Go Ahead with Non-Contrast CTs by Kevin Klauer on next page