Using contrast in patients having abdominal CTs for suspected appendicitis is an ongoing problem. Many radiologists insist on it even when emergency physicians don't want it, it adds hours to the patient evaluation, and it dumps a large oral fluid load on a patient who may be having surgery, increasing the risk of aspiration, at least theoretically. All sorts of literature on this topic indicate that oral contrast adds little if anything to the evaluation when compared with noncontrast CTs, but this topic seems to be highly resistant to the evidence.
Fortunately, at our hospital, the head of radiology agrees with the literature, and when he is on duty, we don't use contrast in these cases. Unfortunately, when he is not on duty, his colleagues are all over the board on this topic, with most saying it is a better study with contrast (sometimes).
Here are two important papers on the topic. The first is a review of 23 studies on using oral contrast in suspected appendicitis in adults. The conclusion of the analysis: The diagnostic performance without oral contrast was at least as good as with it.
A Systematic Review of Whether Oral Contrast is Necessary for the Computed Tomography Diagnosis of Appendicitis in Adults
Anderson BA, et al
Am J Surg
BACKGROUND: Although CT scanning facilitates identifying appendicitis while reducing the risk of negative laparotomy, low rates of CT imaging have been reported. Administration of oral contrast, which can be problematic and prolongs the diagnostic process, might be at least partially responsible for reluctance to request CT scanning for these patients.
METHODS: The authors from the University of Washington in Seattle reviewed the results of 23 studies (19 prospective, 4 retrospective) involving 3,474 patients over age 16 having abdominal CT scanning for suspected appendicitis.
RESULTS: The overall sensitivity, specificity, and diagnostic accuracy were 97%, 97%, and 97%, respectively, for five studies in which scanning was performed with rectal contrast, and 83%, 95%, and 92%, respectively, for two studies in which it was performed with oral contrast. Sensitivity, specificity, and diagnostic accuracy were 95%, 96%, and 96%, respectively, in two studies of scanning with both rectal and oral contrast, and 93%, 93%, and 92%, respectively, in seven studies of scanning with oral plus IV contrast.
In eight studies in which no contrast was utilized, overall sensitivity and specificity were 93% and 98%, respectively, and diagnostic accuracy was 96%. When all studies in which oral contrast was used (alone or with rectal or IV contrast) are compared with studies in which no oral contrast was used, corresponding sensitivities were 92% vs. 95%, specificities were 94% vs. 97%, and diagnostic accuracy was 92% vs. 96%.
CONCLUSIONS: The diagnostic performance of unenhanced CT scanning appears to be at least comparable with scanning protocols requiring oral contrast in patients with suspected appendicitis.
Contrast for Appendicitis?
The second paper addresses a topic that, until recently, I didn't even know was an issue: the use of IV contrast in these cases. IV contrast?! What possible reason could there be for using IV contrast in the patient with suspected appendicitis? I thought IV contrast was about the evaluation of solid organs such as liver, spleen, and kidneys. Recently a colleague ordered both oral and IV contrast in a patient having a CT for suspected appendicitis, and I was very surprised. Using oral contrast is bad enough, but IV contrast is not without risks, particularly if there are issues regarding renal compromise.
The following paper looks specifically at the use of IV contrast to visualize the appendix. The study design was a little unusual, but this is the only study I have come across that addresses this issue. As expected, the use of IV contrast did not significantly improve the visualization of a normal appendix or increase confidence in the CT interpretation by the radiologists.
Normal Appendix in Adults: Reproducibility of Detection with Unenhanced and Contrast-Enhanced MDCT
Keyzer C, et al
Am J Roentgenol
BACKGROUND: Visualization of a normal appendix on CT scanning is believed to reliably exclude appendicitis.
METHODS: This prospective Belgian study examined the effect of IV contrast enhancement and other variables on visualization of a normal appendix in 102 adult cancer patients ages 36 to 94 (mean 63, 74% male) without intraabdominal digestive tumors or suspected appendicitis who were referred for CT evaluation of the abdomen. Each patient underwent 64-multidetector CT scanning with and without IV contrast. CT studies were read independently by two experienced radiologists and one first-year radiology resident. Interpretation of unenhanced and contrast-enhanced CT studies was separated by a two-week period and repeated after one month. The gold standard was interpretation by two independent experts.
RESULTS: The experts identified a normal appendix in 96 percent of the patients. For the three readers, rates of identification of a normal appendix with certainty ranged between 70 percent and 91 percent with unenhanced CT studies, and between 77 percent and 92 percent with contrast-enhanced CT studies. Differences between unenhanced and contrast-enhanced CT studies were not statistically significant. There was perfect intra- and interreader agreement for 71 percent of the patients, and agreement in categorizing confidence in identification of the appendix ranged between fair and good. The level of agreement was influenced by the patients' body mass index and intraabdominal fat volume.
CONCLUSIONS: The level of agreement between radiologists in the visualization of a normal appendix on CT scanning was fair to good. IV contrast enhancement did not significantly improve the visualization of a normal appendix or confidence in CT interpretation.