Adult patients presenting to the emergency department with acute abdominal pain are a daily diagnostic challenge, as there is often a wide differential diagnosis of the cause of the patient's symptoms.1 CT performed in the ED has been shown to have a positive impact on patient management and outcome, although the number of CT procedures performed is often criticized as excessive and older clinicians lament the young physicians' lack of clinical diagnostic skills and their reliance on imaging.

In our recent experience with 536 consecutive CT scans performed in the ED for abdominal pain,2 the three most common pre-CT diagnoses were suspected urinary tract stone (22.5%), appendicitis (17%), and diverticulitis (12.1%). Among the 121 patients presenting with suspected urinary tract stones, 32 (26.4%) were normal or near normal and 70 (57.8%) confirmed the presence of urinary tract stone. An alternative diagnosis was provided by CT in the remaining 19 (15.7%). In only two cases was the final diagnosis appendicitis. Among the 91 patients presenting with suspected appendicitis, 39 (42.9%) were normal or near normal and 29 (31.9%) confirmed the diagnosis of appendicitis. CT provided an alternative diagnosis in 22 (24.2%). In only one case was the final diagnosis a urinary tract stone.

Among patients presenting with these three diagnoses-urinary tract stone, appendicitis, and diverticulitis-we have found that CT had the greatest impact on the management of patients with suspected appendicitis. Performing CT in the ED for these patients eliminated the need for hospital admission in 26/91 (28%) of patients who would have been admitted had CT not been performed. In addition, we have found that performing CT in the ED leads to more timely and appropriate use of surgery. Among the 91 patients with suspected appendicitis, 22 (24%) would have undergone surgery if the CT had not been performed. Following the CT scan, however, only six of those 22 (27%) actually required immediate surgery. Conversely, prior to CT, 69/91 (76%) of patients would not have undergone immediate surgery. CT indicated, however, that 21 of that 69 (30%) actually did require immediate surgery. The net impact of performing CT was to change immediate surgical management in 39/91 (40%) of patients.

Bendeck et al3 have further refined our knowledge of the impact of CT on the management of patients with suspected appendicitis by investigating the differential impact of performing CT on men and women. In a study population composed of 166 women and 178 men who underwent appendectomy, they found that the negative appendectomy rate was significantly lower for women who underwent preoperative CT (6/85, 7%) than for women who did not undergo any preoperative imaging (9/32, 28%). This difference was not found among men, however. The negative appendectomy rate for men who underwent preoperative imaging (5/97, 5%) was not significantly different from that for men who did not undergo any preoperative imaging (2/71, 3%). Based on their data, Bendeck et al conclude:

"Because the negative appendectomy rate was significantly lower in women who underwent preoperative imaging than in those who did not, we propose that imaging be considered part of the routine evaluation of women suspected of having acute appendicitis. Our data suggest that only [men] who have confusing clinical signs and symptoms should undergo preoperative imaging rather than advocate routine imaging for all patients who may have appendicitis."

However, 25/79 (32%) of women and 24/92 (26%) of men who underwent CT were found to have appendiceal perforation.

Recent work by our group4 has shown that the increased use of CT may lead to a significant decrease in surgical-pathological severity of appendiceal disease and hospital stay. We compared two groups of 50 patients each who underwent CT before appendectomy in two time periods, 1997 and 2000. We found that during the three-year time period, the median CT grade of appendicitis decreased significantly from gangrenous or hemorrhagic appendicitis to appendicitis and periappendicitis. This was accompanied by a significant decrease in the mean hospital stay from 2.8 +/- four days in 1997 to 1.5 +/- two days in 2000. The decrease in CT grade of appendicitis parallels an increase in the use of CT during this time period, implying that increased use of CT leads to identification of patients with appendicitis at an earlier stage.

TECHNIQUES

The literature has widely discussed several techniques for imaging the patient with suspected appendicitis. These include the use of oral and/or rectal contrast, IV contrast, focused examination limited to the right lower quadrant, and scanning of the entire abdomen and pelvis. At our institution, we routinely perform CT of the abdomen and pelvis using both oral and IV contrast. The normal appendix can typically be identified in the right lower quadrant 2 to 3 cm below the ileocecal valve. It measures less than 6 mm in diameter and can contain air or oral contrast.

While the identification of the appendix in patients with a moderate amount of intraperitoneal fat is generally not a problem, it can be difficult in young, slender patients whose normal-sized appendix cannot be easily differentiated from small bowel loops. It is therefore important to achieve optimal opacification of small bowel loops with oral contrast, so that a mildly enlarged appendix unopacified by oral contrast can be differentiated from opacified small bowel loops. Thus the oral contrast has to have reached the cecum at the time of the scan. If this is not the case on the initial scan, which is usually obtained one hour after contrast ingestion, a delayed scan after no less than an additional hour should be performed. If this is unsuccessful, further evaluation can be attempted with repeat scanning in the left lateral decubitus position. As the small bowel mesentery falls away from the right side of the abdomen, the appendix is easier to visualize.

Some authors advocate the use of rectal contrast to demonstrate nonfilling of the appendix in acute appendicitis, among other findings. The use of intravenous contrast is very valuable and improves the sensitivity for appendicitis. In particular, in patients with early appendicitis where the appendix is only mildly thickened, intravenous contrast can demonstrate a thickened enhancing wall measuring > 2 mm, which cannot be visualized on a noncontrast enhanced scan.5

CT findings of appendicitis vary depending on the severity of the inflammatory process.6-13 As the time between onset of symptoms and patient presentation to the ER has significantly decreased over the last decade, findings identified on CT have become more subtle.4 An appendiceal diameter greater than or equal to 6 mm is considered abnormal in particular when there is associated "rim" enhancement of the wall and adjacent fat stranding. Inflammatory changes can extend into the cecum and cause cecal wall thickening. As the inflammatory process progresses, a phlegmon develops in the right lower quadrant that can contain extraluminal air in the presence of a perforation. Eventually, abscess formation can be seen as a fluid collection in the right lower quadrant with an enhancing rim that can contain air.

Periappendiceal lymphadenopathy, defined as a short axis diameter of greater than or equal to 6 mm, can be present14 and is an indicator of the severity of the inflammatory reaction. The finding of an appendicolith in the presence of inflammatory changes supports the diagnosis. The significance of an appendicolith as the sole finding in a patient with right lower quadrant pain remains unclear, however.15

As pressures on the healthcare system to provide rapid, cost-effective diagnosis and treatment continue, we expect to see a further reliance on CT imaging to meet these demands. Several studies have already demonstrated that CT is ideally suited to the challenges posed by patients with suspected appendicitis.

Acknowledgment

The author wishes to thank Dr. Bettina Siewert for her thoughtful insights in preparing this article and in participating in our department's research efforts.

References

1. Rosen MP, Sands DZ, Longmaid HE, et al. Impact of abdominal CT n the management of patients presenting to the emergency department with acute abdominal pain. AJR 2000;174:1391-1396.

2. Rosen MP, Siewert B, Sands DZ, et al. Value of abdominal CT in the emergency department for patients with abdominal pain. Eur Radiol 2003;13:418-424.

3. Bendeck SE, Nino-Murcia M, Berry GJ, Jeffrey RB. Imaging for suspected appendicitis: negative appendectomy and perforation rates. Radiology 2002;225:131-136.

4. Raptopoulos V, Katsou G, Rosen MP, et al. Impact of increased use of CT in selecting patients with acute appendicitis earlier. Radiology 2003;226:521-526.

5. Jacobs JE, Birnbaum BA, Macari M. Acute appendicitis: comparison of helical CT diagnosis-focused technique with oral contrast material versus nonfocused technique with oral and intravenous contrast material. Radiology 2001;220:683-690.

6. Balthazar EJ, Megibow AJ, Hulnick D, et al. Computed tomography of the abnormal appendix. JCAT 1988;12:595-601.

7. Applegate KE, Sivit CJ, Salvator AE, et al. Effect of cross-sectional imaging on negative appendectomy and perforation rates in children. Radiology 2001;220:103-107.

8. Gale E, Birnbaum S, Gerzot SG, et al. CT appearance of appendicitis and its local complications. JCAT 1985;9:34-37.

9. Balthazar EJ, Megibow AJ, Siegel SE, Birnbaum BA. Appendicitis: perspective evaluation with high-resolution CT. Radiology 1991;180:21-24.

10. Rao PM, Rhea JT, Novelline RA, Mostafavi AA, et al. Helical CT combined with contrast material administered through the colon for imaging of acute appendicitis. AJR 1997;169:1275-1280.

11. Balthazar EJ, Rofsky NM, Zucker R. Appendicitis: the impact of computed tomography imaging on negative appendectomy and perforation rate. Am J Gastroenterol 1998;93:768-771.

12. Garcia Pena BM, Mandl KD, Kraus SJ, et al. Ultrasonography and limited computed tomography in the diagnosis and management of appendicitis in children. JAMA 1999;282:1041-1046.

13. Kamel IR, Goldberg SN, Keogan MT, et al. Right lower quadrant pain and suspected appendicitis: non-focused appendiceal CT-review of 100 cases. Radiology 2000;217:159-163.

14. Rao PM, Rhea JT, Novelline RA. CT diagnosis of mesenteric adenitis. Radiology 1997; 202:145-149.

15. Lowe LH, Penney MW, Scheker LE, et al. Appendicolith revealed on CT in children with suspected appendicitis: how specific is it in the diagnosis of appendicitis? AJR 2000;175:981-984.

DR. ROSEN is an associate professor of radiology at Harvard Medical School and a radiologist at Beth Israel Deaconess Medical Center in Boston.