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FIGURE 116.3 Perforated appendicitis with abscess and fecalith. Ultrasonography of the pelvis
shows a complex mass (A ) with a fecalith (arrow ) producing characteristic acoustic shadowing
to the right of the bladder (B ).

Initially, the findings may be confused with those of pneumonia because the
extreme abdominal pain may cause rapid shallow respirations, grunting, and
decreased air entry to the lower lung fields. In young children, the findings may
also be confused with meningitis because of paradoxical irritability—any motion
of the child, even trying to comfort the child, may cause pain and irritability.
The laboratory findings in the child with perforated appendicitis often suggest
this diagnosis. The WBC count is significantly elevated, usually higher than
15,000/mm3, with a marked shift to left; leukopenia may be seen with perforation
when associated with overwhelming sepsis.
The radiologic evaluation of suspected perforated appendicitis should include
plain abdominal radiographs and either US, CT, or MRI. The plain film of the
abdomen may show free air or evidence of peritonitis. The US of the pelvis may
show a complex mass with or without a calcified fecalith or free fluid within the
abdominal cavity ( Fig. 116.3 ). CT is generally performed with IV and enteral
contrast to define the size and location of an associated abscess ( Fig. 116.4 ).