Preventing Unnecessary Appendectomies With CT, Ultrasound

Troy Brown

April 16, 2012

April 16, 2012 — Young children and girls older than 10 years appear to have fewer unnecessary appendectomies when diagnostic computerized tomography (CT) and/or ultrasound are used. These imaging techniques appear to have limited value in boys older than 5 years, however, according to a 5-year retrospective review of children with a diagnosis of appendicitis seen in the emergency departments (EDs) of 40 children's hospitals.

Richard G. Bachur, MD, chief of the Division of Emergency Medicine at Children's Hospital Boston, Massachusetts, and colleagues report their findings in an article published online April 16 in Pediatrics.

Dr. Bachur and colleagues determined the accuracy of CT and ultrasound for diagnosing appendicitis by calculating negative appendectomy rates (NARs) for each imaging method, stratified by sex and age (<5 years, 5 - 10 years, and >10 years of age). A negative appendectomy is the surgical removal of a normal appendix.

The researchers wanted to compare CT with ultrasound imaging because CT, which performs better, also exposes patients to ionizing radiation. Because radiation exposure is associated with an increased lifetime cancer risk, ultrasound is an attractive alternative, especially in children.

NARs were calculated by dividing the number of ED patients who underwent appendectomy without a final diagnosis of appendicitis by the total number of ED patients who underwent appendectomy.

The investigators calculated the associations between CT and ultrasound imaging and the outcome of negative appendectomy using linear regression analysis that used the hospital-level NAR as the dependent variable and the hospital-level imaging rate as the independent variable, weighted by the number of appendectomies done at each hospital. They performed this analysis on each age and sex subgroup, adjusting for patient volume at each institution.

From a total of 8,959,155 ED visits, 55,227 children were given a final diagnosis of appendicitis. Of those children, 35,335 (64.0%) had uncomplicated appendicitis, 13,166 (23.8%) had a perforated appendix, and 6.26 (12.2%) had a perforated appendix with abscess formation. Of the 52,290 patients who underwent an appendectomy, 96.4% received a final diagnosis of appendicitis, leaving a NAR of 3.6%.

Hospital-Level Analysis

CT rates were higher than ultrasound rates for each sex and age subgroup. In each subgroup, girls received more imaging than boys did, and children younger than 5 years were most likely to undergo both CT and ultrasound. The highest NARs were in children younger than 5 years and girls older than 10 years. There was a significant association between rate of CT and/or ultrasound use by individual institutions and the institutional NAR in all subgroups except children younger than 5 years. The CT rate alone was not associated with institutional NAR for any subgroup studied. The lowest NARs were found in boys older than 5 years, regardless of imaging method.

Patient-Level Analysis

Boys older than 5 years have lower NARs than boys younger than 5 years. Preappendectomy CT was significantly associated with lower NARs in boys younger than 5 years only, and ultrasound use was associated with higher NARs in boys younger than 5 years.

In girls younger than 5 years, CT was significantly associated with lower NARs, but there was no difference in NAR if ultrasound was used.

NARs were significantly higher in girls older than 10 years (5.5%) compared with boys (1.1%), independent of imaging (adjusted odds ratio, 5.2; 95% confidence interval, 4.4 - 6.1).

The Bottom Line

"The current study's findings extends to the clinical management by suggesting that age and gender must be incorporated into any evaluation algorithms," the authors write.

Because boys older than 5 years have the lowest NARs regardless of imaging method, the authors feel that CT and ultrasound imaging have limited value in this subgroup. "Of note, the paradoxically higher NAR for boys younger than 5 years who had an ultrasound (compared with those who did not have an ultrasound) might reflect an attempt to rely on ultrasound over CT when the diagnosis is especially difficult in this age group," the authors write.

"[T]he higher NAR for those girls older than 10 years likely stems from the presence of gynecologic conditions where secondary findings noted by imaging may mimic appendicitis," write the authors. "Despite this relatively high rate of negative appendectomy, the use of imaging among postpubertal girls is associated with the greatest absolute reduction in negative appendectomies as previously recognized," they write.

The authors conclude that CT and ultrasound reduce the higher NARs found in children younger than 5 years and girls older than 10 years, but appear to be of limited value in boys older than 5 years with suspected appendicitis and no other clinical issues.

The authors have disclosed no relevant financial relationships.

Pediatrics. Published online April 16, 2012.

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