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Findings: Enlarged (diameter = 9 mm) noncompressible, hyperemic appendix with periappendiceal fluid as well as fluid within the pouch of Douglas c/w acute appendicitis.

Diagnosis: Acute appendicitis.

Discussion: Acute appendicitis is the most common indication for emergency laparotomy in children. Perforation, although still uncommon, occurs with a much greater frequency (approximately 25%) in the pediatric population. The pathogenesis generally begins with luminal obstruction. Continued natural secretions of mucus within the appendix leads to distention. Luminal bacteria multiply as venous engorgement develops secondary to the elevated intraluminal pressure causing vascular compromise. Finally, arterial compromise ensues and perforation occurs with the development of a periappendiceal abscess.

The usual initial symptoms are vague visceral abdominal pain secondary to the distention of the appendix. After 4 to 6 hours, as the inflammation spreads to the parietal peritoneum, the pain increases in intensity and becomes somatic in nature localized at "McBurney's Point" in the RLQ. Nausea, vomiting, and anorexia are frequently associated. The typical historical and physical findings are found in approximately 2/3 of patients eventually determined to have appendicitis. The clinical diagnosis is not always entirely straightforward especially in children who may not be able to communicate their symptoms adequately. Imaging methods must be used in patients with indeterminate clinical findings to avoid unnecessary laparotomies.

Ultrasound is the current diagnostic modality of choice in children judged to have low or intermediate probability of appendicitis based on clinical findings. A cross-sectional diameter measurement of greater than 6 mm along with noncompressibility in a patient with persistent RLQ pain is considered reliable evidence of appendicitis. It is extremely important that the entire appendix is visualized because inflammation may be localized to the distal tip. Associated findings include loss of the echogenic submucosal layer which may reflect extension of the inflammation through the muscularis propria. There may be a fluid-filled lumen which will be anechoic and/or a hyperechoic appendicolith with acoustic shadowing. There may also be associated periappendiceal fluid collections or mass which may displace adjacent structures. These latter findings are more likely to be seen in association with perforation.

References:
Sivit CJ. Diagnosis of Acute Appendicitis in Children: Spectrum of Sonographic Findings.
AJR. 1993;161:147-152.2. Sivit CJ, et al. Appendicitis: Usefulness of US in Diagnosis
in a Pediatric Population. Radiology. 1992;185:549-552.

Siegel MJ. Acute Appendicitis in Childhood: The role of US. Radiology. 1992;185:341-342.

Gore RM, Levine MS, Laufer I. Textbook of Gastrointestinal Radiology. Philadelphia, PA:
W. B. Saunders Co;1994;1474-1475.

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