Abdominal pain duration influences appendicitis imaging diagnosis

Aug 14 2012

By Liam Davenport, MedWire Reporter

Clinicians should not rely on ultrasonography for diagnosing pediatric appendicitis early in the course of illness, say US researchers.

They found that the sensitivity and negative predictive value of ultrasonography improved with longer duration of abdominal pain, whereas computed tomography (CT) demonstrated high sensitivity regardless of pain duration.

The researchers, led by Richard Bachur, from Harvard Medical School in Boston, Massachusetts, therefore suggest that "when an ultrasonographic result is obtained and negative, clinicians might choose a period of observation, potentially followed by repeated ultrasonography (or CT) if clinical suspicion remains."

While CT sensitivity was unaffected by abdominal pain duration, results were less likely to be equivocal with longer abdominal pain duration, the team notes.

A total of 1810 children, aged 10.9 years on average, with suspected appendicitis underwent CT or ultrasonography as part of a prospective multicenter observational study.

The team reports in the Annals of Emergency Medicine that the duration of abdominal pain was less than 72 hours in all cases, and imaging studies were performed within 8 hours of having undergone clinical examination. In all, 1216 children had CT and 832 underwent ultrasonography.

Appendicitis was diagnosed in 680 patients, of whom 174 had perforated appendicitis. The duration of abdominal pain was most commonly 12‑23 hours. The risk for perforated appendicitis increased significantly with increasing abdominal pain duration.

The sensitivity of ultrasonography for diagnosing appendicitis increased linearly with increasing pain duration, from 79% for pain duration of less than 12 hours to 96% for pain duration of 48‑71 hours. By contrast, CT sensitivity and the specificity of either modality was unaffected by pain duration.

The researchers note, however, that the proportion of equivocal CT readings decreased significantly with increasing pain duration, from approximately 7.5% for pain duration of less than 12 hours to around 2.0% for pain duration of 48‑71 hours.

The researchers conclude: "The performance of CT and ultrasonography for accurately identifying appendicitis is influenced by the duration of abdominal pain… Clinicians should incorporate this time-dependent accuracy of imaging when deciding to obtain imaging for suspected appendicitis."

In an accompanying editorial, Gregory Connors and Lisa Schroeder, from the University of Missouri in Kansas City, say that the changing sensitivity of ultrasonography with pain duration is important: "First, it instructs clinicians caring for children with abdominal pain that negative ultrasonography study results are less reliable for detecting appendicitis early in the course of illness… Second, this finding reminds us that studies reporting just 1 value for a test's sensitivity or specificity may be incomplete."

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