You just heard a great lecture on minimizing radiation exposure from diagnostic testing and your next patient may give you the opportunity to put the lecturer’s plan into practice. The patient is a 19-year-old male who thinks he may have food poisoning due to the fact that he developed abdominal pain last night after eating a burrito at a local “Roach Coach”. He said it tasted fine, but soon after developed abdominal pain in his right lower abdomen. He denies any fever, vomiting, nausea or diarrhea, but did say he hasn’t been hungry this morning. The pain is constant, non-migratory and is gradually getting worse. He motions to a specific localized area with two fingers as he describes the pain. The pain has been present for about 14 hours. He tried some Pepto-Bismol but it didn’t help, but at least hasn’t caused any dark stool or salicylate induced duodenal ulcers.
On exam the patient has normal vital signs with a temperature of 98.2°F. There is no scleral icterus and his exam is essentially normal except for some tenderness to palpation in one small area in the right lower quadrant. Rovsing’s sing is negative. You check a psoas sign to check for retrocecal appendix inflammation and it is also negative. Thinking back to the lecture you just heard you wonder if this is a patient that your surgeon might take to the OR without the almost obligatory CT scan of the abdomen. You order labs and even consider adding a sed-rate, hoping if it is high it might buff your argument to skip the CT if the white count happens to come back normal. Finally, you place a call to your surgeon. You explain to the patient that you plan to give him some pain medication, but if the pain is only mild, it might be better to wait until you talk to the surgeon. You also briefly explain the risks and benefits of having surgery versus having a CT scan first. You don’t want him to think you are cutting corners or rushing so you make sure to tell him that it is always safer for you as a doctor to do more tests and you are more than happy to do it if he wants, but that you think it is safer for him to dodge the radiation bullet in this instance.
You weigh things in your head. The history and exam are not necessarily “textbook classic” but they are pretty suggestive, and you don’t really suspect any alternative diagnosis. The history of progressively worsening right lower quadrant pain, focal RLQ tenderness and the absence of ovaries are, in your mind, the most important elements of the true triad for acute appendicitis, even if the patient doesn’t have many associated symptoms. As you are mulling all of this over in your head, the on-call surgeon calls back. You make your case, emphasizing that this is a young patient and that avoiding radiation is therefore more important than in an older patient. The surgeon agrees with your reasoning, but states that he recently read a study that shows that CT scans decreases the risk of a negative laparotomy. (No duh, you think to yourself). He says, “Hold off on the CT for now. I’m upstairs. I’ll be down in fifteen minutes.”
Your labs come back ten minutes later showing a white count of 12.1 with 75% PMN’s. Unfortunately, you wish you hadn’t ordered the sed rate because it was only 5. The surgeon waltzes in just then, says hi, and sees the patient. Your optimism barometer takes a small dive when he comes out of the room and requests a CT scan. “Why try?” you think to yourself. It’s easier to just do what everyone else does; it’s harder to do the right thing. With your bubble burst, you walk back to your desk and your white coat accidentally catches on one of the handles of the ED ultrasound machine, catapults it across the floor right into the room the surgeon came from. The plug flies off the holder and miraculously makes a flawless entry into the wall outlet and turns itself on. You look down at the floor and see the bottle of ultrasound gel spinning at your feet. Could this be some sort of a sign?
“Hey Steve,” you say to your surgical colleague. “Have you ever used an ultrasound machine before to look for appendicitis?” You know his answer – neither have you, but maybe today is the day. You log onto EMresource.org to refresh your memory (shameless plug) and get some quick tips and then obtain the image shown above.
The surgeon is standing right next to you as you obtain the image. What does he say? Conclusion on NEXT page
Dx: The No-CT Appy
The surgeon is right beside you as you pull up the images. “Let’s forget the CT. That sure looks like a swollen appendix to me,” he says. An hour later he walks back through the ED and pats you on the back. “You were right,” he says, then adds, “Hey, am I allowed to use that machine in the future?”
Tips & Tricks for
IMAGING THE APPENDIX
01 Benefits of Ultrasound: Using ultrasound to diagnose acute appendicitis has many benefits. It avoids both radiation and IV contrast and their small, but real, associated risks. In addition, ultrasound may be faster than CT as there is no need to wait for BUN & creatinine results or for oral contrast to move distally, if you are still one of those people who do full contrast CTs. If you do the ultrasound yourself it is even faster!
02 Sensitivity & Specificity: Both the sensitivity & specificity of ultrasound for appendicitis are less than that of CT. In pediatrics the values are about 88% and 94% respectively, and in adults about 83% and 93%. (These numbers may vary depending on the experience of the ultrasonographer.) There are studies from Europe and Israel where they have used the “ultrasound first” approach for many, many years that show even better test characteristics. These values are actually not that bad when compared to CT scan whose sensitivity and specificity are around 94% and 95% respectively. Remember, however, that the performance characteristics for ultrasound can be significantly worse in overweight patients or those with overlying bowel gas. In addition, if the appendix is retrocecal or is lying in a difficult anatomical plane, the study will be more challenging. Unfortunately, you may still have to do a CT scan if your ultrasound is non-diagnostic and your clinical suspicion is moderate to high, but the strategy of ultrasound first would likely decrease CTs by about 50%.
03 Patient Selection: Ultrasound is an excellent initial imaging modality for the appendix in thin individuals, especially children and young adults. The lower amount of interfering subcutaneous fat and heightened concern over unnecessary radiation in this population makes them optimal candidates for ultrasound instead of, or at least before, CT. In the pregnant patient, ultrasound is the initial study of choice to evaluate right-lower-quadrant pain and can be performed simultaneously with a pelvic scan to look for a cyst, mass, free fluid, or ectopic pregnancy.
04 Probe Selection: In most patients, use a 7.5-10 MHz linear array probe. If the appendix is superficial in a thin patient, you may be surprised at just how easy it is to find. For deeper imaging, you may need to obtain images with the 3-5 MHz curvilinear probe. Consider this probe in patients with increased subcutaneous fat, or those in whom a retrocecal appendix is suspected. Be advised, the further the appendix is from your probe the more challenging your imaging will be.
05 Technique Tips: Allow the patient to direct the ultrasound probe to the point of maximal tenderness. Begin your scan there. Look for a non-compressible round structure about 1cm in diameter. Always image in at least two planes: once you find a cross-sectional view of what appears to be an inflamed appendix, adjust your probe to look for a long-axis view. Confirm that the structure has a blind-tip at one end to avoid confusion with vascular or other structures. In some cases, you may also see a hyperechoic appendicolith with posterior shadowing.
06 Diagnostic Criteria: Diagnostic criteria for acute appendicitis are as follows: a non-compressible, aperistaltic blind-ended tubular structure which is greater than 7mm in diameter and connects to the cecum. Checking for non-compressibility involves pushing down with the ultrasound probe to see if the structure you are viewing is flattened at all. Intestines usually will demonstrate peristalsis which can be seen in real time if you look long enough.
07 Other Signs: On a transverse image of the appendix, look for the “target sign” of inflamed muscularis propria surrounded by edema and inflammatory changes. You might see other sonographic clues, including periappendiceal fluid, prominent pericecal fat with stranding, a hyperechoic appendicolith within the tubular appendix, or presence of an abscess or phlegmon.
08 Negative Studies: You or your friendly sonographer must visualize a normal, compressible appendix on ultrasound to definitively rule-out appendicitis. Unlike with CT scan, this is rarely the case. If the appendix is not seen on ultrasound, you have a non-diagnostic study, so consider an 8-hour return visit for ongoing pain, a surgical consultation, or a CT scan.
09 Know Thy Surgeon: Not all surgeons are comfortable going to the OR based on an ultrasound that is positive for appendicitis. If the pretest probability is not already very high, your surgical colleagues may still request a CT scan. Don’t let that prevent you from doing the right thing for your patient. If you do more ultrasounds you and/or your ultrasound techs will become more proficient and your surgeons will eventually get more comfortable when repeated ultrasounds are confirmed by either CT or operative findings. If you impress your surgeons, they may even want to start borrowing your machine to do their own ultrasounds.
10 Disadvantages: Ultrasound is far less likely to accurately identify other causes of right lower quadrant pain such as a kidney stone, Crohn’s disease, right sided diverticulitis and mesenteric adenitis. Keep this and your differential diagnosis and relative levels of suspicion in mind when choosing your initial imaging study.
11 Pediatrics: You should be aware of the most recent recommendation of the American College of Radiology from the “Choosing Wisely” campaign, which states, “Don’t do computed tomography (CT) for the evaluation of suspected appendicitis in children until after ultrasound has been considered as an option.” Although CT is accurate in the evaluation of suspected appendicitis in the pediatric population, ultrasound is nearly as good in experienced hands. Since ultrasound will reduce radiation exposure, ultrasound is the preferred initial consideration for imaging examination in children. If the results of the ultrasound exam are equivocal, it may be followed by CT. This approach is cost-effective, reduces potential radiation risks and has excellent accuracy, with reported sensitivity and specificity of 94 percent.
Brady Pregerson (@TheSafetyDoc) manages a free online EM Ultrasound Image Library and is the editor of the Emergency Medicine Pocketbook series. For more info visit EMresource.org.
Teresa S. Wu (@TeresaWuMD) is the Associate Residency Director, and Director of Ultrasound and Simulation Programs and Fellowships, for the Maricopa EM Program in Phoenix.