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
Counter: Go Ahead with Non-Contrast CTs
Safely Saves Time and Money
by Kevin Klauer, DO
Contrast protocols, including intravenous, oral and/or rectal contrast, are just not necessary for abdominal CTs. From my perspective, the only emergent CTs that warrant IV contrast administration are CT pulmonary angiograms to identify pulmonary emboli, chest or abdominal CTs to investigate suspicion for aortic dissection and perhaps for blunt abdominal trauma.
Several studies have shown the accuracy of unenhanced or non-contrast studies. Their accuracy has been proven for almost any intra-abdominal process you could consider.
Keyzer reported in 2009 that in 131 patients, comparing oral and IV protocols to IV only, visualization of the appendix was dependant upon the reader not the protocol (AJR Am J Roentgenol. 2009 Nov;193(5):1272-81.). Beyond the concept of inter-reader variability is the fact that unenhanced studies are very accurate and are becoming more so as technology continues to improve. In 1999, Lane reported unenhanced CTs to be 96% sensitive and 99% specific for appendicitis in 300 consecutive ED patients suspected of having appendicitis (Radiology 213:341, 1999.). In 2002, the British Journal of Radiology reported the same findings in 108 patients with surgically proven appendicitis. The sensitivity of unenhanced CTs with 5mm sections was 96% sensitive and 98% specific for appendicitis (Br J Radiol. 2002 Sep;75(897):721-5.). Some have reported that with less intra-abdominal fat, visualization of the appendix is more difficult in pediatrics, necessitating contrast to discern the appendix from other structures. Hoecker, at the Children’s Hospital of San Diego, reported no difference in the accuracy of unenhanced CT, compared to findings for enhanced CTs reported by previous studies. They reported the positive and negative predictive value to be 91.3% and 90.8%, respectively.
Hill, from Michigan State University, confirmed that for all non-traumatic intra-abdominal processes, there was no statistical difference between enhanced and unenhanced studies for making the correct diagnosis (World J Surg. 2010 Apr;34(4):699-703.), and Tack reported similar findings for the diagnosis of diverticulitis (Radiology. 2005 Oct;237(1):189-96.).
Although suggesting a place for IV contrast, the use of oral contrast provides no benefit for detecting bowel or mesenteric injuries (J Trauma. 2004 Feb;56(2):314-22.). No evidence refutes the value of IV contrast for splenic and hepatic vascular injuries, reserving a place for its use in trauma.
The situation changes if the concern is for an intra-abdominal vascular catastrophe. Some clinicians mistakenly interchange the terms aortic dissection, a separation of the intima from the media, and aneurysm. Although dissections can sometimes be associated with aneurysms, these two diagnoses are very different. You can have a leaking or ruptured AAA without a dissection, and you can have a dissecting aorta without any aneurysmal dilatation. Thus, if you are looking for a dissection, you need intravenous contrast to show the false lumen (separation) between the intima and the media. Not so for aneurysms, as a dilated aorta can be easily seen without contrast. Blood from a leaking or ruptured AAA is evident without any contrast. The blood is contrast enough.
The real controversy in the use of oral and/or rectal contrast exists with abdominal/pelvic studies. Radiologists report the increased sensitivity of 64 and 128-slice MDCT scanners and warn us constantly of hypersensitivity reactions, albeit less likely with non-ionic contrast, and contrast-induced nephrotoxicity. And yet, they still want us to use contrast to “improve imaging quality.” If they want to limit the risk of acute hypersensitivity reactions and nephrotoxicity, they need to quit demanding contrast when the evidence just doesn’t support its use.
In addition to posing additional unnecessary risk to the patient, using contrast also causes substantial operational issues in every emergency department, resulting in increased throughput times, diagnostic delays and less patients being seen. For example, if an oral contrast protocol takes 90 minutes to complete (delivery, ingestion of the contrast and waiting for it to traverse the GI tract) and 10 ED patients undergo this protocol daily, a cascading effect of delays will result. Those ten protocols will cost your department 15 hours of bed time. This equates to 5,475 hours annually. If the average length of stay (all comers) is two hours, 2,737 less patients can be seen in your department annually, resulting in $273,700 less physician reimbursement (assuming an average $100 collected per patient) and $1,095,000 less revenue for the hospital in ED charges alone (assuming an average of $400 per visit for the facility/hospital side).
So if the contrast is not clinically necessary, per the research, and it’s obstructing the ED, why are we still doing it? The radiologists claim they get better results. However, their own literature suggests that they don’t. To quote Rick Bukata: If we put their own literature in a Mercedes catalog, maybe they’ll read it. The fact is that whatever marginal benefit in image quality is perceived by some Radiologists is most likely personal preference and is so minor that it doesn’t aid them in getting the right answer.
There are limitations to CT with any abdominal process. However, the use of contrast doesn’t remedy those concerns. It has been proposed that we should just order “renal stone protocol CTs” and avoid the argument altogether. I don’t advocate this approach for two reasons. First, without disclosing what pathology we are truly looking for, we are handicapping the Radiologist, impairing their ability to appropriately interpret the study. If you’re worried about appendicitis, they need to know that. The second reason is that we shouldn’t hide from this discussion. If we stop calling this practice into question, I fear it will be accepted as standard practice, resulting in delays, ED inefficiency and potential patient complications.