Factors Contributing to Nonvisualization of the Appendix on Ultrasound in Children With Suspected Appendicitis.

OBJECTIVE: This study aimed to identify the patient characteristics, history factors, physical examination findings, and sonographic findings, which contribute to a higher risk of the appendix not being visualized on ultrasound evaluation (ie, nondiagnostic or equivocal study) in patients being evaluated for appendicitis. Secondarily, this study assessed the utility of an equivocal ultrasound, specifically in the ability to predict the absence of appendicitis. METHODS: A retrospective case review was performed, of children (age, 0-18 years) presenting to a pediatric emergency department with clinical suspicion for appendicitis, who underwent sonographic studies during the 12-month study period. RESULTS: Five hundred forty-three cases were reviewed, of which 75 (14%) were diagnosed with appendicitis. The sensitivity of ultrasound diagnosis of appendicitis was 62.7% and specificity was 79.1%. The appendix was not visualized in 398 (73%) cases. Of the cases where the appendix was not visualized, 370 did not have appendicitis (negative predictive value, 93%). In cases where the appendix was not visualized and the white blood cell count was less than 10,000, the negative predictive value rose to 97%. The patient's age (odds ratio [OR], 1.049), weight (OR, 1.015), presence of appendicolith (OR, 0.426), presence of right lower quadrant fat stranding on sonography (OR, 0.081), and presence of hyperemia on sonography (OR, 0.094) were found to be significant in affecting the visualization of the appendix on ultrasound. CONCLUSIONS: Increasing patient's age and weight leads to increased likelihood that the appendix will not be visualized on ultrasound, whereas the presence of an appendicolith, right lower quadrant fat stranding or hyperemia will increase the likelihood of visualization. The sensitivity and specificity of ultrasound for the diagnosis of appendicitis are moderate but the negative predictive value of an equivocal study is high. Clinicians can use supporting clinical examination and laboratory findings, in conjunction with a nondiagnostic ultrasound evaluation of the appendix to exclude the diagnosis of appendicitis, without the need for further imaging.