Focused CT using a height-adjusted metric and the umbilicus as a landmark for children undergoing evaluation for appendicitis.

backgroundConfirmation of appendicitis in children often requires CT. A focused CT scan that is limited to the lower abdomen/pelvis might help to reduce radiation exposure.

objectiveTo determine the position of the appendix relative to the umbilicus and derive a height-adjusted threshold for a focused CT that would identify most appendices. MATERIALS AND

methodsWe conducted a retrospective study of children younger than 18 years who underwent a CT scan for suspected appendicitis. A pediatric radiologist determined the distance from the most cephalad portion of the appendix to the center of the umbilicus. This distance was divided by the child's height to create a ratio for each child. We then assessed the largest of these distance/height ratios ("height constants") as potential height-adjusted thresholds that, when multiplied by any patient's height, would yield the superior threshold for the focused CT scan. Radiation reduction was calculated as percentage decrease in scan length compared to a complete abdominopelvic CT.

resultsOf 270 patients whose entire appendix was identified on CT, all were identified within 10.5 cm above the umbilicus. A focused CT using a height constant of 0.07 identified 100% of the appendices visualized on the complete CT scan and resulted in an estimated mean percentage radiation reduction of 27% (standard deviation [SD] +/-4.7). If a height constant of 0.03 was used, 97% of appendices were identified and the estimated radiation reduction was 43% (SD +/-4.3).

conclusionA height-adjusted focused abdominopelvic CT scan might reduce radiation exposure without sacrificing the diagnostic accuracy of the complete CT scan.