Clinicians frequently order lab tests in children with suspected appendicitis. Urine should be tested for infection but the presence of pyuria does not exclude the diagnosis of appendicitis. The white blood cell (WBC) count is typically obtained, but it is nonspecific and insensitive for appendicitis. Its sensitivity increases with longer duration of symptoms and with perforation. Some decision rules, however, have found that a normal to low WBC count does help stratify a population of children who are at low risk of acute appendicitis.3,4
Radiography is rarely helpful in the diagnosis of appendicitis unless an appendicolith is seen. Many surgeons will proceed directly to surgery without further imaging if the remainder of the presentation is consistent.
Ultrasound (Fig. 50-1), despite lower sensitivity and specificity than computed tomography (CT) for appendicitis, is the initial diagnostic imaging modality of choice because of concern regarding radiation exposure.5 Pooled estimates of sensitivity and specificity have been reported to be 88% and 94%, respectively.6 However, more recent reports do not show such high sensitivities. The ability to identify the appendix on ultrasound improved with time, and sensitivities were as low as 61% when done “after hours.” Sensitivity varies with the duration of symptoms with it being lower early on (∼80%) and rising to near 100% as the disease progresses.7 Thus, both operator experience and timing of symptoms play a role in the utility of ultrasound. Children early in the course of disease should have strategies that rely on observation, serial examination, repeat ultrasounds, or CT scans if indicated. If the ultrasound is not definitive, then a CT should be done.
Acute appendicitis. A noncompressible, inflamed appendix is shown. A. A cross-sectional view (7.5 MHz). B. A longitudinal section (7.5 MHz). Mural lamination of the swollen appendix is maintained in the early stages of acute appendicitis. C. An appendicolith (arrow) with acoustic shadowing is demonstrated (5 MHz). D. A focal loss of mural lamination in the appendiceal tip (arrows) is demonstrated as a result of gangrene (9 MHz).
CT (Fig. 50-2) has sensitivity and specificity in the mid- to high 90s.6–8 The choice of contrast for these CTs varies according to institution-specific guidelines, but has not been shown to impact the test characteristics significantly.9 One must consult with their local radiologists to ensure that the ionizing radiation levels used are the lowest needed for adequate images. MRI is now being studied, and ultrafast MRI without sedation is promising as another radiation-sparing imaging modality.10
CT scan with oral and intravenous contrast of acute appendicitis. There is thickening of the wall of the appendix and periappendiceal stranding (arrow).
Scoring Systems and Clinical Decision Rules
In recent years, the development and attempted validation of pediatric appendicitis scoring systems and clinical prediction rules have increased. The most frequently used scoring systems are the Alvarado score and the Samuel score.11,12 Preliminary data from the development cohorts were promising, but subsequent validation studies have shown mixed results.13–18 There is utility at the extremes of scores. These are scores of children in whom the presence or absence of appendicitis is not difficult. Not surprisingly, these scoring systems are less reliable in clinically challenging patients.
Clinical prediction rules have been developed but attempts at validation have been challenging. Kharbanda et al. have described the following prospectively validated prediction rule: an absolute neutrophil count of 6.75 × 103/μL or less and no maximal tenderness in the right lower quadrant, or an absolute neutrophil count of 6.75 × 103/μL or less with maximal tenderness in the right lower quadrant but no abdominal pain with walking, jumping, or coughing. This refined rule had a sensitivity of 98.1%, specificity of 23.7%, and negative predictive value of 95.3%.4
No scoring system or clinical prediction rule can completely exclude or completely make the diagnosis of appendicitis without a small percentage of children undergoing a negative appendectomy. The data do, however, provide the practitioner some strategies to avoid immediate imaging, especially CT scan, and observe a subset of patients that are at low risk.