Can a computed tomography (CT) scan of the abdomen and pelvis without intravenous contrast (IV contrast) detect acute appendicitis?

From the Guidelines

Yes, a CT scan of the abdomen and pelvis without contrast can effectively detect appendicitis, with a sensitivity of 0.90 (95% CI: 0.86-0.92) and a specificity of 0.94 (95% CI: 0.92-0.97) as reported in a meta-analysis of prospective studies 1. This imaging technique is commonly used in emergency settings to diagnose appendicitis with high accuracy, typically around 90-95%. The scan can reveal key findings such as an enlarged appendix (greater than 6-7mm in diameter), appendiceal wall thickening, periappendiceal fat stranding, and the presence of an appendicolith (calcified deposit within the appendix). While contrast-enhanced CT scans may provide additional information in certain cases, non-contrast CT is often sufficient for diagnosis and is particularly valuable for patients who cannot receive contrast due to kidney problems or allergies. It also offers advantages including quicker scan time, no need for contrast preparation, and reduced risk of adverse reactions. However, interpretation depends on radiologist expertise, and some early cases of appendicitis might be missed. In pregnant patients or children, ultrasound is typically tried first to avoid radiation exposure, with CT reserved for cases where ultrasound results are inconclusive. According to the most recent guidelines, CT without IV contrast also has high diagnostic accuracy in detecting acute appendicitis and may be appropriate 1. Some key signs of appendicitis on CT include maximal outer diameter >6 mm, fat stranding, and absence of intraluminal gas, with the presence of two or more signs increasing the odds ratio of appendicitis being present 1. Overall, non-contrast CT is a reliable and efficient imaging modality for diagnosing appendicitis, especially in emergency settings where timely diagnosis is crucial. The use of non-contrast CT can help reduce the risk of complications associated with delayed diagnosis and treatment, such as perforation and abscess formation, ultimately improving patient outcomes and quality of life. In clinical practice, the decision to use non-contrast CT should be based on individual patient factors, including the presence of kidney disease or allergies, and the clinical suspicion of appendicitis. By prioritizing the use of non-contrast CT in appropriate cases, clinicians can provide high-quality care while minimizing the risks associated with contrast administration. In addition, the use of non-contrast CT can help reduce healthcare costs and improve resource utilization, making it a valuable tool in the diagnosis and management of appendicitis. Overall, the evidence supports the use of non-contrast CT as a first-line imaging modality for suspected appendicitis, with contrast-enhanced CT reserved for cases where additional information is needed or where non-contrast CT is inconclusive.

From the Research

CT Abdomen Pelvis Without Contrast for Detecting Appendicitis

• The diagnostic accuracy of non-enhanced CT (NECT) for detecting acute appendicitis has been compared to contrast-enhanced CT (CECT) in several studies 2, 3.
• A study published in 2021 found that NECT had a sensitivity of 80.7%, specificity of 86.7%, and accuracy of 84.3% for diagnosing acute appendicitis, which was comparable to CECT 2.
• Another study published in 2019 found that unenhanced CT had a lower sensitivity (0.91) compared to CT with intravenous contrast (0.96), but the difference in specificity was negligible 3.
• The use of oral contrast in CT scans for suspected appendicitis in children did not improve diagnostic accuracy, and its use is not warranted 4.
• Low-dose CT has been shown to be accurate in identifying appendicitis and differentiating between uncomplicated and complicated acute appendicitis, with a significant reduction in radiation dose compared to standard-dose CT 5.

Key Findings

• NECT can detect appendicitis with comparable accuracy to CECT in some cases 2.
• The sensitivity of unenhanced CT may be lower than CT with intravenous contrast, but the difference in specificity is negligible 3.
• Low-dose CT is a viable option for reducing radiation dose while maintaining diagnostic accuracy 5.