What imaging modality is best for urgently ruling out both nephrolithiasis (kidney stones) and acute appendicitis?

From the Guidelines

For urgent evaluation of both kidney stones and appendicitis, a noncontrast CT scan of the abdomen and pelvis is the recommended initial imaging modality, as it can effectively assess kidney stones without the need for IV contrast, which may obscure small renal stones, and also provide diagnostic information for appendicitis, with a sensitivity of 90% and specificity of 96% for noncontrast CT in diagnosing appendicitis 1.

Key Considerations

• Noncontrast CT is the preferred initial test for evaluating kidney stones, as it can detect stones without the need for IV contrast, which may obscure small renal stones 1.
• For appendicitis, noncontrast CT has been shown to be conclusive in up to 75% of cases, with a reported sensitivity of 90% and specificity of 96% 1.
• If the initial noncontrast CT is inconclusive, a contrast-enhanced CT may be necessary to further evaluate for appendicitis, with a sensitivity of 95.6% and specificity of 92.3% 1.
• Ultrasound may be considered as an alternative initial imaging study, particularly in patients where radiation exposure is a concern, such as pregnant patients or children, but it has lower sensitivity for both conditions, with a pooled sensitivity of 83% for appendicitis and a sensitivity of 52-57% for renal stones 1.

Imaging Modalities

• Noncontrast CT: preferred initial test for kidney stones and appendicitis, due to its high sensitivity and specificity for both conditions 1.
• Contrast-enhanced CT: may be necessary if initial noncontrast CT is inconclusive, particularly for appendicitis, due to its high sensitivity and specificity 1.
• Ultrasound: alternative initial imaging study, particularly in patients where radiation exposure is a concern, but has lower sensitivity for both conditions 1.

Clinical Implications

• The choice of imaging modality should be based on the clinical presentation and suspicion of kidney stones or appendicitis, as well as the patient's individual risk factors and concerns, such as radiation exposure 1.
• A comprehensive evaluation with a single test, such as noncontrast CT, can reduce time to diagnosis and improve patient outcomes, particularly in emergency settings where prompt treatment decisions are crucial 1.

From the Research

Imaging for Urgent Rule Out of Both Kidney Stones and Appendicitis

• The diagnosis of acute appendicitis and kidney stones can be challenging, and imaging plays a crucial role in making an accurate diagnosis 2, 3.
• Computed Tomography (CT) is often used as an add-on test following the initial evaluation to reduce remaining diagnostic uncertainty for suspected appendicitis 3.
• For diagnosing acute appendicitis, the sensitivity and specificity of CT are high, with summary sensitivity of 0.95 and summary specificity of 0.94 3.
• Non-enhanced CT appears to have lower sensitivity than standard-dose CT with intravenous, rectal, or oral and intravenous contrast enhancement for diagnosing appendicitis 3, 4.
• However, some studies suggest that non-enhanced CT can provide comparable diagnostic accuracy to contrast-enhanced CT for diagnosing acute appendicitis, especially when at least 3 imaging findings are present 5.
• For kidney stones, non-contrast CT is the preferred imaging modality, as it can detect stones with high sensitivity and specificity.
• A study comparing non-enhanced CT with contrast-enhanced CT for the diagnosis of acute appendicitis found no significant difference in diagnostic accuracy between the two techniques 5.
• The use of oral contrast in CT scans for suspected appendicitis in children does not improve diagnostic accuracy and can increase wait time 6.

CT Findings for Appendicitis

• Appendiceal dilatation (appendiceal diameter ≥7 mm) and the presence of appendicoliths are specific imaging findings on CT that can identify patients with acute appendicitis 2.
• CT findings of appendicolith, mass effect, and a dilated appendix greater than 13 mm are associated with a higher risk of treatment failure with an antibiotics-first approach 2.
• The presence of at least 3 imaging findings on non-enhanced CT or at least 4 on contrast-enhanced CT can provide the best diagnostic accuracy for acute appendicitis 5.

Recommendations for Imaging

• For patients with suspected appendicitis, CT with intravenous contrast is recommended as the initial imaging modality, unless contraindicated 3, 4.
• Non-enhanced CT can be considered as an alternative for patients who cannot receive intravenous contrast, as it can provide comparable diagnostic accuracy 5.
• For patients with suspected kidney stones, non-contrast CT is the preferred imaging modality.