| Discussion: |
Appendicitis is an acute inflammation of the appendix. The appendix is a blind-ending diverticular structure arising from the cecum. Acute appendicitis is a common cause of abdominal pain and the most frequent condition leading to emergent abdominal surgery in pediatrics. The pathophysiology of appendicitis is due to a closed loop obstruction of the appendix.
Obstruction may be secondary to impacted fecal material or hyperplasia of the submucosal lymphoid follicles. Obstruction of the appendiceal lumen leads to mucosal edema, increasing intraluminal pressure and exudate from the appendix. When the exudate touches the parietal peritoneum, it leads to a more intense and localized pain, usually in the right lower quadrant. As the obstruction persists, bacteria within the appendix proliferate, enhancing the inflammatory response and further increasing the intraluminal pressure. If the diagnosis of appendicitis is not made early, the obstruction will progress, the wall of the appendix will stretch due to the further rise in intraluminal pressure, and perforation will occur.
When the inflammatory fluid and bacterial contents are released into the abdominal cavity, peritonitis develops. Concomitantly, the patient will complain of more intense and generalized abdominal pain.
In adults and adolescents, the omentum can wall off the inflamed or perforated appendix, causing a focal abscess. In the younger child, the omentum is less well developed and less likely to wall off a perforation, making peritonitis more likely.
It is important to understand the typical clinical manifestations of appendicitis in order to make an early and accurate diagnosis prior to perforation. The classic history of anorexia and periumbilical pain, followed by right lower quadrant pain and vomiting, is observed in fewer than 60% of cases.
Abdominal radiograph findings are normal in many cases of acute appendicitis. The presence of a calcified appendiceal fecalith occurs in fewer than 10% of cases.
Ultrasound is the preferred imaging modality in the evaluation of acute appendicitis in pediatrics. The advantages of ultrasound include its noninvasiveness, lack of radiation, no contrast medium, and minimal pain.
One disadvantage is that the examination in operator-dependent. Ultrasound examination has had an overall sensitivity of 85% and specificity of 94% in pediatric patients in experienced hands. The finding of a noncompressible dilated appendix is a strong indicator of nonperforated appendicitis. After perforation, ultrasound can identify a periappendiceal phlegmon or abscess formation. Additional findings that can support the diagnosis of appendicitis include the presence of appendicoliths, fluid in the appendiceal lumen, focal tenderness over the inflamed appendix, and a transverse diameter of 6 mm or more.
In 1997, Lane evaluated helical CT scanning without contrast and found a sensitivity of 90% and specificity of 97%. A more recent (1999) study of noncontrast helical CT in 300 adult patients with suspected appendicitis found sensitivity of 96% and specificity of 99%. Two studies of focused helical CT in children suggest sensitivity of 95% in that population.
CT findings diagnostic of acute appendicitis are a distended appendix (>6 mm in diameter), thickened walls that enhance, and periappendiceal inflammatory changes with stranding in the fat. Complications associated with perforated appendicitis include phlegmon, seen as a periappendiceal soft tissue mass and abcess. Phlegmons and abcesses < 3cm in size usually resolve with antibiotic therapy, while those > 3cm usually require surgical or catheter drainage. A calcified appendicolith can be seen in about 25% of cases.