The use of CT as a diagnostic tool in pediatric acute appendicitis is increasing because of its high sensitivity and specificity. However, due to both the serious concerns about radiation of CT and the convenience and reasonable cost of ultrasound (US) examination, US has value on the initial diagnosis of acute appendicitis despite of the lower sensitivity in children. The purpose of this study was to examine the factors that affect the rate of false negative diagnosis of the ultrasound from the patients who received laparoscopic appendectomy.

The pediatric appendectomy cases from 2002 to 2013 in Yeouido St. Mary's Hospital have been reviewed through the medical records. We included patients who underwent an initial screening by ultrasound examination.

Among 181 patients, 156 patients were the sono-positive group and 25 patients were sono-negative group. There is no significant difference in ages, genders, physical examination findings and white blood cell count between the two groups. But, the degree of inflammation of appendicitis (simple, 58.3% vs. 32.0%; complicated, 41.7% vs. 68.0%) and the appendix position (antececal, 85.0% vs. 12.0%; retrocecal, 13.7% vs. 44.0%; pelvic, 1.3% vs. 44.0%) were significantly different between the two groups (sono-positive group vs. sono-negative group; p<0.05).

The position of the appendix may act as a factor that causes an error in the diagnostic ultrasound, especially, in the retrocecal type and the pelvic type with the higher risk of necrosis or perforation.