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Ultrasound Before CT in Patients with Acute Abdominal Pain

A diagnostic strategy of ultrasound followed by CT only if ultrasound results are nondiagnostic optimizes sensitivity while minimizing radiation exposure.

Early diagnostic computed tomography (CT) in patients with acute abdominal pain increases detection of serious diagnoses but is time-consuming and costly and can increase risk for future cancers from radiation exposure (JW Emerg Med Apr 24 2009). To identify an optimal imaging strategy, researchers prospectively collected data for 1021 hemodynamically stable, nonpregnant adult patients (mean age, 47; 55% female) with nontraumatic acute abdominal pain (duration, 2 hours to 5 days) who presented to six emergency departments in the Netherlands. All patients were evaluated by a radiologist with a structured imaging protocol consisting of plain x-rays (upright chest and supine abdomen), ultrasonography, and CT.

At 6 months, an expert physician panel determined the final diagnosis and classified it as urgent (requiring treatment within 24 hours; 65% of patients) or nonurgent. The most common urgent final diagnosis was acute appendicitis (28%), followed by acute diverticulitis (12%). Investigators compared the sensitivity and specificity of 11 diagnostic imaging strategies for detecting conditions classified as urgent. Clinical diagnosis was highly sensitive (88%) but nonspecific, with and without the addition of plain x-rays (specificity, 43% and 41%, respectively). Ultrasound reduced the rate of false-positive urgent diagnoses, but its sensitivity was only 70%. CT had a sensitivity of 89%. Sensitivity was highest (94%) with a conditional strategy of using CT only after nondiagnostic ultrasound; only half the patients would have required CT with this strategy.

Comment: This elegant study provides strong evidence for use of a strategy that optimizes sensitivity while minimizing radiation exposure for evaluation of acute abdominal pain in nonpregnant adults: ultrasound first, followed by CT only if ultrasound results are negative or inconclusive. Of note, intravenous contrast alone was used for CT; thus, CT studies need not be delayed for administration of oral contrast. As shown in many prior studies, plain radiographs are essentially useless, except perhaps to confirm a diagnosis of acute bowel obstruction.

— Kristi L. Koenig, MD, FACEP

Published in Journal Watch Emergency Medicine July 24, 2009

Citation(s):

Laméris W et al. Imaging strategies for detection of urgent conditions in patients with acute abdominal pain: Diagnostic accuracy study. BMJ 2009 Jun 26; 338:b2431. (http://dx.doi.org/10.1136/bmj.b2431)

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• Medline abstract (Free)

Dixon AK and Watson CJ. Imaging in patients with acute abdominal pain. BMJ 2009 Jun 26; 338:b1678. (http://dx.doi.org/10.1136/bmj.b1678)

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• Medline abstract (Free)

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• US before CT in acute Abdomen
  K.D. Bhargava, Indore India, 1 Aug 2009 12:54 AM EST
  Good History with good Gen Examination quite often suffices to recognize genuine urgency. In less previeledged countries, CBC and US... [more]