Appendix not seen: the predictive value of secondary inflammatory sonographic signs

Acute appendicitis is the most prevalent emergency surgical diagnosis in children. Although traditionally a clinical diagnosis, the diagnosis of acute appendicitis is uncertain in approximately 30% of pediatric patients. In attempts to avoid a misdiagnosis and facilitate earlier definitive care, imaging modalities such as ultrasonography have become important tools. In many pediatric studies, the absence of a visualized appendix with no secondary sonographic features has been reported as a negative study result, and a study where the appendix is not seen but demonstrates secondary features is often deemed equivocal. With ultrasound appendiceal detection rates reported at 60% to 89%, the dilemma of the nonvisualized appendix or equivocal study is frequently faced by clinicians.

This study aimed to assess the value of the nonvisualized appendix on ultrasound and the association of secondary sonographic findings in pediatric patients with acute right lower quadrant pain undergoing ultrasound, in whom acute appendicitis was a diagnostic consideration.

Retrospective case review of 662 consecutive children (age < 18 years) presenting to a pediatric emergency department with clinically suspected appendicitis, who had graded compression sonographic studies during the 24-month study period, was performed.

The appendix could not be visualized in 241 studies (37.7%). An alternate diagnosis was identified via sonography in 47 patients (19.5%). Twenty-five patients (12.9%) were taken for surgery where 17 (8.8%) had acute appendicitis confirmed via pathology. The specificity of moderate-to-large amounts of free fluid is 98%, phlegmon at 100%, pericecal inflammatory fat changes at 98%, and any free fluids with prominent lymph nodes at 81%. The odds ratio of appendicitis increases from 0.56 to 0.64 to 2.3 and 17.5, respectively, when there were 2 and 3 ultrasonographic inflammatory markers identified.

Although uncommonly seen, large amounts of free fluid, phlegmon, and pericecal inflammatory fat changes were very specific signs of acute appendicitis. In the absence of a distinctly visualized appendix, the presence of multiple secondary inflammatory changes provides increasing support of a diagnosis of acute appendicitis.