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Pediatric Imaging

E3027. Pinworms and Other Pitfalls in Ultrasound of Pediatric Appendicitis

Desai S1,2,  Lee A1,2,  Bray H.1,2 1. BC Children's Hospital, Vancouver, Canada; 2. University of British Columbia, Vancouver, Canada

Address correspondence to S. Desai (

Background Information: Acute appendicitis is a common cause of acute abdominal pain in children. Abdominal ultrasound, in conjunction with clinical assessment and laboratory testing, is a valuable and commonly used diagnostic tool in children with suspected appendicitis. Primary sonographic criteria for the diagnosis of appendicitis are visualization of a noncompressible appendix with a diameter greater than 6 mm. Secondary features of appendiceal inflammation add confidence to the sonographic diagnosis. Pinworm infestation of the appendix and other processes can result in an enlarged noncompressible appendix or secondary signs of appendiceal inflammation, mimicking appendicitis. These pitfalls, if not recognized, may lead to a falsely positive ultrasound study and unnecessary appendectomy.

Educational Goals/Teaching Points: We review and illustrate the primary and secondary ultrasound features of acute appendicitis in children; review and illustrate other pathologic processes that may mimic the sonographic appearance of appendicitis in children, with correlative histological and gross specimen images; and emphasize the importance of presence of both primary and secondary sonographic features of appendicitis to confidently diagnose acute appendicitis in children and avoid the potential pitfalls.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: Key imaging findings and challenges: Traditional criteria for ultrasound diagnosis of appendicitis (i.e., > 6 mm diameter, noncompressible) alone are insufficient evidence of acute appendicitis. Presence of additional sonographic features improves specificity and diagnostic confidence. These secondary features include: thickened, echogenic mesenteric fat circumferential to the appendix; loss of the bowel wall signature in the appendix, with nonvisualization of alternating hyperechoic mucosal and hypoechoic submucosal layer; and presence of an appendicolith. Other processes, such as infestation by pinworms (Enterobius vermicularis), mimic appendicitis sonographically by causing distension of the appendiceal lumen. Lymphoid hyperplasia causes thickening of the hypoechoic lamina propria of the wall of appendix, resulting in increased appendiceal diameter. Granulomatous inflammation of the appendicitis in Crohn disease or Yersinia infection also results in a thickened appendiceal wall. Meckel diverticulitis can mimic acute appendicitis as the inflamed Meckel diverticulum may be visualized on ultrasound as a distended blind-ending tube. Omental infarction results in thickened and echogenic mesenteric fat in the right lower quadrant. The sonographic appearance of these potential pitfalls will be illustrated with correlative gross surgical and histologic specimens.

Conclusion: Attention to both primary and secondary features of appendiceal inflammation in children is important to improve diagnostic confidence and specificity and to recognize pitfalls that may lead to unnecessary appendectomy.