Ultrasound for pediatric appendicitis offers no-dose alternative to CT

December 2, 2005

In many institutions, children with suspected appendicitis head straight to the CT scanner for evaluation. Ultrasound provides an alternative, accurate means of making an initial diagnosis, sparing many children from potentially harmful radiation exposure, according to a study presented at the RSNA meeting on Friday.

In many institutions, children with suspected appendicitis head straight to the CT scanner for evaluation. Ultrasound provides an alternative, accurate means of making an initial diagnosis, sparing many children from potentially harmful radiation exposure, according to a study presented at the RSNA meeting on Friday.

In a retrospective study of 129 patients with suspected appendicitis, ultrasound as the primary imaging modality accurately identified positive cases and spared 45% of patients from CT radiation exposure, said Shlomit Goldberg, a medical student at Stanford who presented the results.

"Appendicitis is extremely common in children. The number of pediatric CT scans is increasing rapidly, despite evidence that children are in the highest risk group for cancer related to radiation exposure," Goldberg said.

Many researchers have been looking into ways of lowering dose of pediatric CT studies to reduce risks. Another option is to eliminate unnecessary exams that expose children to radiation.

In order to use CT more sparingly, Stanford has developed protocols for handling pediatric patients who present with appendicitis. Ultrasound has a high positive predictive value in pediatric appendicitis and can be relied upon to identify patients who need surgery.

But it also has a high false negative rate. Therefore, according to the protocol, ultrasound is the primary imaging modality for pediatric appendicitis and positive cases on diagnostic ultrasound are sent to the operating room for surgery. But indeterminate or negative ultrasound studies are followed up with CT.

Researchers performed a retrospective study of cases handled between January 2003 and February 2005 to assess how well the triage system was working. They compared histopathology to the diagnoses made with ultrasound and CT. In all 32 patients who had ultrasound and then went to surgery, histopathology correlated with the positive ultrasound diagnosis.

In another study presented at the RSNA meeting, pediatric radiologists shared experience with eliminating oral contrast in rapid low-dose helical CT scans of pediatric appendicitis patients. Results were presented by Dr Lori Barr, a diagnostic radiologist in Austin, TX.

Oral contrast can be unpleasant for children. Some find it difficult to consume, and become nauseous. In some cases, it may be necessary to intubate in order to administer the contrast. Another drawback of oral contrast is time: the preparation process takes one hour, which is inefficient for the health system and more difficult for the patient.

Pediatric radiologists introduced a rapid CT scanning protocol for scanning the abdomen and pelvis without contrast on a four-slice scanner. They performed a prospective study to see if they could safely switch to a faster method of diagnosis without sacrificing accuracy.

"When you have a two-year-old on a CT table, the shorter the scan time the better," Barr said. "And if you can take them into a room and have them on and off the table in a matter of minutes, that is a huge difference compared to what we had to do in the past."

The children in the study ranged in age from seven months to 16 years. They presented to the emergency room with acute abdominal pain between January and June 2004.

The study included 107 scans performed on 100 patients. Sensitivity and specificity without oral contrast were 100% and 95% respectively, compared to 100% and 94% for studies with oral contrast. The small difference in specificity was not statistically significant.

In rapid studies performed on a multislice scanner, administration of oral contrast makes no difference in the detection of acute appendicitis in children, researchers concluded.

Radiologists have been wary of scanning without contrast, as the appendix is difficult to visualize. But the study found that secondary findings, such as fluid in the pelvis, easily enabled diagnosis, reducing the necessity of visualizing the appendix.

The new protocol has proven popular all around.

"The success has been phenomenal. It's a great technique and it works for everyone-- clinicians, patients, and parents are very happy," Barr said.

However, given the ease-of-use and quality of the rapid, low-dose CT scan, there are still concerns about over-utilization of CT in the emergency room and unnecessary radiation exposure.

"There is nothing to stop an emergency room doctor from doing multiple CT scans. Our hope is that we have provided a technique that will answer clinical questions, but we still want doctors to be judicious and first use clinical skills to make a diagnosis," Barr said. "They should only use CT when they can't figure out the diagnosis clinically or by another noninvasive means, like ultrasound."

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