Abdominal pain is a common presenting symptom, accounting for nearly 7 percent of emergency department visits in 2005. Although the diagnosis of acute appendicitis is often straightforward, some patients may have early or atypical signs and symptoms that make the diagnosis more challenging. Despite the increasing use of computed tomography (CT) in patients with suspected appendicitis, such widespread use may not be necessary. Clinical indicators, such as laboratory findings and patient signs and symptoms, can help determine which patients with abdominal pain require abdominal CT.

The American College of Emergency Physicians (ACEP) has developed evidence-based recommendations to help physicians judge which clinical findings are most useful for guiding decision making in patients with suspected acute appendicitis. The guidelines also address the use of contrast dye in imaging and the choice of imaging modality in children.

Clinical Findings

Not every patient with suspected acute appendicitis requires abdominal imaging. Clinical findings should be used to risk stratify patients to guide decisions about further testing, including the need for CT. Right lower quadrant abdominal pain is the most helpful clinical sign; pain migration and progression are less helpful. Laboratory testing should include both a white blood cell count and a C-reactive protein level. Neither test consistently confirms or excludes the diagnosis of acute appendicitis when used alone.

The Alvarado score combines clinical and laboratory findings to assign a score from 0 to 10 (Table 1). Theoretically, higher Alvarado scores are associated with a higher likelihood of appendicitis. However, it is unclear whether the score can reliably predict the need for CT, and imaging is recommended even in patients with low scores.

The diagnosis of acute appendicitis is challenging in children, especially in infants and toddlers. Missed or delayed diagnosis can result in perforation, which can cause longer hospital stays, bowel obstruction, and sepsis. Five findings that are consistently associated with appendicitis have been identified in children: nausea, focal right lower quadrant abdominal pain, difficulty walking, rebound tenderness, and an absolute neutrophil count of greater than 6,750 cells per mm³ (6.75 × 10⁹ per L).

Contrast Dye

Once the decision is made to use imaging to help diagnose acute appendicitis, physicians must determine whether to use contrast dye. Intravenous contrast dye highlights inflammation in the wall of the appendix and in the tissue around the appendix; enteric contrast dye helps differentiate the appendix from the surrounding structures. However, oral contrast dye requires time to administer and to transit the bowel, and patients with abdominal pain and vomiting may not tolerate it. Although rectal contrast dye requires less time, patients may find it uncomfortable or unacceptable. Intravenous contrast dye may lead to a severe allergic reaction or renal failure.

In most studies of abdominal and pelvic CT for the evaluation of acute appendicitis in adults, CT performed reasonably well, regardless of whether contrast dye was used. The addition of enteric and intravenous contrast dye improves diagnostic accuracy, but only by a small degree, and the use of oral contrast dye confers no diagnostic benefit.

Diagnostic Imaging in Children

Abdominal and pelvic CT can be used in children to confirm or rule out acute appendicitis. However, CT is expensive and exposes the patient to ionizing radiation. For these reasons, physicians should consider using ultrasonography as the initial imaging modality. Ultrasonography is fast, safe, well tolerated, and does not expose the patient to radiation. It can confirm the diagnosis of acute appendicitis in children, but it cannot definitively rule out the condition. If the diagnosis remains uncertain after ultrasonography, CT can be performed.