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There are a number of possible causes of severe abdominal pain of sudden onset. Increasingly, computed tomography (CT) and ultrasound (US) are being found extremely valuable in assessing the causes, and determining the appropriate treatment (in particular whether surgery is needed, and determining when and how that surgery should most appropriately be done). Also, CT may serve as a "roadmap" for planning surgery or planning a CT or US guided drainage procedure. As with other CT imaging studies, CT of the abdomen and pelvis has been even further enhanced with the advent of multidetector row CT, which provides a more rapid acquisition of a 3-D volume of data, and provides even greater options in terms of resolution and image processing. (see Multidetector Row CT page)
Causes of abdominal pain which may be detected on CT include:
- Appendicitis
- Bowel Obstruction
- Cholecystitis
- Pancreatitis
- Pyelonephritis
- Renal stone disease (if suspected, can initially scan without contrast)
- Diverticulitis
- Inflamed Meckel's Diverticulum
- Epiploic Appendigitis
- Omental Infarction
- Crohn's Disease
- Mesenteric Adenitis
- Acute gynecologic disorders: ovarian cysts, PID/TOA, torsion, ectopic
Appendicitis
A very common serious cause of acute abdominal pain is appendicitis. There are 250,000 new cases each year in United States. This condition has traditionally been most often diagnosed on clinical grounds. However, classic signs and symptoms of appendicitis are often not present in patients with appendicitis, and a delay in diagnosis increases risk of appendiceal perforation & increased risk of post-op complications. On the other hand, the appendix is normal in 15-40% of patients who undergo emergent appendectomy, meaning unnecessary surgery.
CT and Ultrasound (US) are the most useful imaging techniques for acute abdominal pain. Advantages of CT include:
- more accurate in staging periappendiceal inflammation & abscesses
- more likely to provide alternate diagnosis in patients without appendicitis
- more sensitive for detecting normal appendix
- operator independent
- not limited by pt body habitus
(See Figures 1-3 for examples of appendicitis on CT)
Ultrasound (Figure 4), although with these limitations compared to CT, is appropriate to consider for pregnant women or children (avoid radiation), or as an adjunct to CT, especially when CT suggests equivocal findings of possible appendicitis in a location easily amenable to further assessment with US, or when gynecologic pathology is suspected in reproductive-age females.
Numerous reports have now shown very high accuracy (94-98%) for detecting or excluding appendicitis by CT. In an internal review of recent patients with suspected appendicitis, for whom CT was performed prior to surgery, physicians in Madison Radiologists were found to have similar accuracy.
CT may also impact on therapy for appendicitis. CT is useful in cases of perforation for distinguishing between phlegmon & abscess. Antibiotics with nonsurgical approach may be most appropriate if periappendiceal phlegmon or small abscess is found. In the case of a liquified abscess, a more well-localized collection may undergo percutaneous drainage, whereas immediate surgical exploration with drainage & appendectomy are indicated if abscess formation is extensive & poorly defined. CT also provides an accurate "road map" for determining proper approach for surgical or percutaneous drainage.
Effect of CT on Treatment & Use of Hospital Resources in Appendicitis
100 consecutive pts with suspected appendicitis underwent appendiceal CT53 had appendicitis, & 47 did not.
Accuracy of CT 98% (compared with much lower accuracy even of an experienced surgeon).
Use of CT resulted in prevention of unnecessary surgery in 13 pts & unnecessary hospital admission for 50 pt-days.
Cost savings of $20,250 ($447 per pt).
{Rao et al., NEJM 1998; 338:141-146}
Small Bowel Obstruction
Small bowel obstruction (SBO) is a common occurrence, and it is important that the site, level, severity, and cause of obstruction be accurately determined in order for SBO to be properly treated. Often surgery can be avoided in patients with incomplete bowel obstruction, and CT can greatly help select those for whom surgery is necessary, as well as provide critical information in planning for surgery. CT is increasingly being utilized as the first imaging test when SBO is suspected. Besides confirming or excluding the diagnosis, and demonstrating the site, level, and severity of obstruction if present, CT can often allow determination of the cause (Figure 5) and detection of complications of obstruction (such as ischemia and perforation) that mandate surgical intervention. (Cooper, Daneshmand, Boudiaf, Burkill, Zalcman) CT has been shown to be superior to small bowel follow-through for detecting the cause of intestinal obstruction and presence of strangulation. (Peck) CT has also been shown to be both sensitive and specific in diagnosing small bowel obstruction in children. (Jabra)
Spiral CT - Ureteral Calculi
Spiral CT of the abdomen and pelvis without contrast has been increasing in use for evaluation of suspected kidney stones (Figure 6a & b). Advantages over the traditional method of intravenous urogram include shorter time to diagnosis, greater sensitivity for seeing small stones in the kidneys, ureter and bladder, providing an alternative diagnosis if the patient does not have a kidney stone as the cause of pain, and the lack of need for injecting intravenous contrast.
Diverticulitis
The clinical diagnosis of diverticulitis (inflammation & perforation of colonic out-pouchings, or diverticula), is often uncertain and frequently incorrect. While the diagnosis may often be made with contrast enema or colonoscopy, CT offers a rapid, noninvasive, accurate method of diagnosing diverticulitis and its complications (Figure 7), as well as alternative diagnoses. It is more sensitive than a contrast enema for diagnosing diverticulitis, and allows demonstration of an abscess if present, which may require surgical or percutaneous drainage.
Case Studies
References
1. Ahn Sh, Mayo-Smith WW, Murphy BL, Reinert SE, Cronan JJ. Acute nontraumatic abdominal pain in adult patients: abdominal radiography compared with CT evaluation. Radiology 2002; 225:159-64.
2. Rao PM, Boland GWL. Imaging of acute right lower abdominal quadrant pain. Clin Radiology 1998; 53:639-649.
3. Birnbaum BA and Jeffrey RB. CT and sonographic evaluation of acute right lower quadrant abdominal pain. AJR 1998; 170:361-371.
4. Naoum JJ, Mileski WJ, Daller JA, Gomez GA, Gore DC, Kimbrough
5. Puylaert JBCM, Rutgers PH, Lalisang RI, et al. A prospective study of ultrasonography in the diagnosis of appendicitis. New Engl J Med 1987; 317:66-669.
6. Rao PM, Rhea JT, Novelline RA, et al. Helical CT technique for the diagnosis of appendicitis: Prospective evaluation of a focused appendix CT examination. Radiology 1997; 202:139-144.
7. Balthazar EJ, Birnbaum BA, Yee J, Megibow AJ, Roshkow J, Gray C. Acute appendicitis: CT and US correlation in 100 patients. Radiology 1994; 190:31-35.
8. Lane MJ, Katz DS, Ross BA, Clautice-Engle TL, Mindelzun RE, Jeffrey RB. Unenhanced helical CT for suspected acute appendicitis. AJR 1997;168:405-409.
9. Rao PM, Rhea JT, Novelline RA, Mostafavi AA, McCabe CJ. Effect of computed tomography of the appendix on treatment of patients and use of hospital resources. New Engl J Med 1998; 338:141-146.
10. Smith RC, Verga M, McCarthy S, Rosenfield AT. Diagnosis of acute flank pain: Value of unenhanced helical CT. AJR 1996; 166:97-101.
11. Smith RC, Verga M, McCarthy S, Rosenfield AT. Acute ureteral obstruction: Value of secondary signs of helical unenhanced CT. AJR 1996; 167:1109-1113.
12. Katz DS, Lane MJ, Sommer FG. Unenhanced helical CT of ureteral stones: incidence of associated urinary tract findings. AJR 1996;166:1319-1322.
13. Fielding JR, Silverman SG, Samuel S, Zou KH, Loughlin KR. Unenhanced helical CT of ureteral stones: A replacement for excretory urography in planning treatment. AJR 1998; 171:1051-1053.
14. Rao PM. CT of diverticulitis and alternative conditions. Semin Ultrasound CT MR 1999; 20:86-93.
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