From the Guidelines
A CT scan of the abdomen and pelvis without IV contrast can be used to diagnose appendicitis, with a reported sensitivity of 90% and specificity of 96% in a study of 536 patients 1. The evaluation of appendicitis with a nonenhanced CT was shown to be conclusive in up to 75% of cases, with a reported positive predictive value (PPV) and negative predictive value (NPV) of 84.8% and 97.4%, respectively 1. However, in inconclusive cases, the initial noncontrast CT study was followed by contrast-enhanced CT with a sensitivity, specificity PPV, and NPV of 95.6%, 92.3%, 73%, and 99%, respectively 1. Some key points to consider when using a non-contrast CT to diagnose appendicitis include:
- The inflamed appendix may appear enlarged and thickened on a non-contrast CT
- Surrounding inflammatory changes like fat stranding or free fluid might be visible
- The absence of IV contrast may limit the diagnostic accuracy, especially in cases where the appendix is not clearly visible
- Other findings like appendicolith, periappendiceal fat stranding, or appendiceal enlargement become more important diagnostic indicators in the absence of IV contrast 1.
From the Research
CT Scan with Abdomen Pelvis without IV Contrast for Appendicitis
- A CT scan with abdomen pelvis without IV contrast can show appendicitis, as studies have found that nonenhanced CT (NECT) has comparable diagnostic accuracy to contrast-enhanced CT (CECT) for diagnosing acute appendicitis 2.
- The sensitivity, specificity, and accuracy of NECT for diagnosing acute appendicitis were found to be 80.7%, 86.7%, and 84.3%, respectively, which are similar to the values for CECT 2.
- Another study found that low-dose unenhanced CT is equal to standard-dose CT with intravenous contrast agents in the detection of signs of acute appendicitis 3.
Comparison with Other Imaging Modalities
- Ultrasound (US) is often used as the first-line imaging test for suspected appendicitis, but CT is superior to US and is required immediately in patients with atypical clinical presentation of appendicitis and suspected perforation 3.
- A systematic review and meta-analysis found that CT has higher sensitivity and specificity than US for diagnosing acute appendicitis, with pooled sensitivity and specificity for CT of 0.972 and 0.956, respectively, and 0.821 and 0.859 for US, respectively 4.
Diagnostic Accuracy
- The diagnostic accuracy of CT for acute appendicitis can be improved by using at least 3 imaging findings for NECT or at least 4 for CECT, and by using a cut-off threshold of 9.25 mm for the detection of patients with acute appendicitis 2.
- Enteral contrast does not improve the diagnostic performance of CT for suspected appendicitis, and IV contrast alone is sufficient 5.