Appendiceal phlegmon mimicking intussusception on ultrasound: correspondence between sonographic and operative findings.

Little is known about the possibility that ruptured appendicitis may produce a false sonographic appearance of intussusception. We present here a case of a periappendiceal phlegmon mimicking ileocolic intussusception on ultrasound in a 3.5-year-old girl and provide a surgico-anatomic explanation on the basis of the intraoperative findings for the false sonographic image. CT imaging was used to make the diagnosis. Intraoperatively, it was revealed that the cecum and sigmoid, which were adherent to each other with pseudomembranes, formed an intestinal mass around the appendix. Accordingly, the appendicolith at the center of the phlegmon was responsible for the central echogenicity, and the surrounding cecum and sigmoid for the external hypoechoic and hyperechoic rings of the target-sign appearing mass on the preoperative ultrasound. Such an understanding of the etiology of the false sonographic image may help to increase awareness and avoid misdiagnosis.