Thursday, November 15, 2007

To CT or Not to CT? Another Salvo

Common things being common, anyone who has spent a little time perusing medical blogs has read a few posts about the value, or lack thereof, of CT scans in the evaluation of suspected acute appendicitis. I'll outline my opinions below (Opinions? Moi?), but there has been another salvo fired in this skirmish, this time aimed against the "CT everyone" crowd.

A study published in this month's Journal of Gastrointestinal Surgery from the University of Wisconsin asks the question Computed Tomography in the Diagnosis of Acute Appendicitis: Definitive or Detrimental? This was a retrospective study of all adult patients treated for acute appendicitis at their institution over a three year period. Any imaging results were correlated with operative findings, including the presence or absence of perforation of the appendix.

Results During a 3-year period, 411 patients underwent appendectomy for presumed acute appendicitis at our institution. Of these patients, 256 (62%) underwent preoperative CT, and the remaining 155 (38%) patients did not have imaging before the surgery. The time interval between arrival in the emergency room to time in the operating room was longer for patients who had preoperative imaging (8.2 ± 0.3 h) compared to those who did not (5.1 ± 0.2 h, p < 0.001). Moreover, this possible delay in intervention was associated with a higher rate of appendiceal perforation in the CT group (17 versus 8%, p = 0.017).
Although retrospective, this study gives a bit more ammunition to the "CT very selectively" crowd. It appears that CT scanning delayed operative intervention in most patients, and that was the supposed reason for a higher rate of perforation in the patients who underwent CT. Ergo, they say, use CT scanning less in cases of suspected appendicitis. Sounds logical, no?

Hold your horses, Kemo Sabe. There's a whole lotta supposition going on there, so let's look a little deeper into the data, shall we? In the article, a few interesting things become apparent:
  • While the majority of patients were male, a higher percentage of those undergoing CT were female. That's just plain reasonable, because women have those little things called tubes and ovaries that can be troubled and cause symptoms like appendicitis.
  • Those patients who had an "indeterminate" scan were lumped in with the "negative" scan patients. This is because the scan in those cases did not enhance the ability for the clinician to make a diagnosis.
  • 8% of those diagnosed with appendicitis on CT had a normal appendix removed at surgery. That's plain interesting, because CT has been touted as nearly perfect at diagnosing acute appendicitis when it's called "positive" by the radiologist.
  • 14% of those taken to the OR for presumed appendicitis without preop CT had a normal appendix. I'd say that's within historical norms, and actually a bit lower than I would have anticipated --- plus, it's not statistically different than those that had CT scans.
  • 7 of 14 patients with negative CT scans were ultimately found to have appendicitis; as a result, when evaluating both the negative and indeterminate CT scan results together, the negative appendectomy rate was 37% (leaving us, for those with statistical interest, an overall sensitivity of 92%, specificity of 68%, accuracy of 88%, and a negative predictive value of less than 40%). Hmmm. What we don't know is the true denominator of this number -- this is a small sample of patients who had a negative CT, as presumably the majority were sent on their merry way and never had any difficulties. It is interesting, however, that 14 patients with negative CTs made their way to the OR for presumed appendicitis, and half of them had it despite the CT findings.
  • The majority of perforations were not identified on CT. That's reasonable, as most of the time a small perforation is found at surgery. What is not spelled out is how many patients had a CT because of generalized peritonitis, which could have a variety of possible causes and for which a CT is often a good idea.
  • Interestingly, the study did not identify patients thought to have appendicitis on CT, who were found to have some other pathology. That is presumably because they only looked retrospectively at those patients identified by procedure codes as undergoing appendectomy.
Well, let's think a bit about this. At least at the University of Wisconsin, a CT scan is reasonably accurate for diagnosing appendicitis, but it sure ain't perfect. Well, what's an ED physician to do? IMHO, it's time to put a little common sense back into play --- the immediate availability of an abdominal CT scan does not justify its (over)use, so here are the Aggravated DocSurg guidelines for diagnosing appendicitis, with and without CT:
  • Young men with right lower quadrant pain, tenderness, and an elevated white blood cell count need to be poked and prodded by a surgeon, not sent through an irradiating donut.
  • Young women with right lower quadrant (not pelvic) pain, tenderness, and an elevated white blood cell count need to be poked and prodded by a surgeon, and then possibly sent through an irradiating donut.
  • Older men and women with right lower quadrant pain, tenderness, and an elevated white blood cell count need to be poked and prodded by a surgeon, not sent through an irradiating donut.
  • If there is any other combination of symptoms --- pain not in the "classic" location, a normal white blood cell count, a suspicion of diverticulitis/nephrolithiasis/PID --- by all means get a CT.
  • Never, ever (ever!) get a CT of the abdomen without oral contrast when there is even the slightest possibility that the patient may have GI tract pathology, including appendicitis (for some reason, that's en vogue in my hospital) --- it's worthless, and may require your patient to undergo a second round of radiation.
  • Last but not least, when in doubt, get a CT.
Wait a minute. Didn't someone who sounds a bit like me just say, "the immediate availability of an abdominal CT scan does not justify its (over)use?" Er, yes. And I also just said, "when in doubt, get a CT." I'm sorry, I know that makes me sound a little like Zaphod Beeblebrox, but one has to keep in mind that not every patient has read the textbook and presents like "classic" appendicitis. And I would prefer that ED physicians feel that the CT is a readily available part of the armamentarium they have at their disposal in evaluating abdominal pain --- but they should also should stick to their guns and ask surgeons to come evaluate patients who have likely appendicitis, and not be cowed into obtaining a CT every time just because the surgeon insists on it.

All I ask is for the ED physician to let "surgeon versus CT evaluation" cross his or her mind a little more frequently before asking for a CT. At least according to this study, it will save your patients time and possibly avoid an increased risk for perforation if the surgeon is involved early ---- plus, you can always punt the question of CT or no CT to him after he evaluates the patient.