Comparison of Non-Contrast CT vs. Contrast-Enhanced CT with Both Intravenous and Rectal Contrast Application for Diagnosis of Acute Colonic Diverticulitis: A Multireader, Retrospective Single-Center Study

Abstract

Objectives: To evaluate the non-inferiority of non-contrast CT compared to contrast-enhanced CT with both intravenous and rectal contrast application for the diagnosis of acute colonic diverticulitis. Methods: Five readers retrospectively evaluated the non-contrast and contrast-enhanced series of CTs of 205 consecutive patients with clinical suspicion of acute diverticulitis. Two randomized reading sessions, both containing all 205 cases as either contrast-enhanced or non-contrast (1:1) series, were performed with ≥8 weeks washout between them. The non-inferiority margin was set to 0.1. Results: The pooled prevalence (all readers) of diverticulitis was similar for non-contrast CT (63.9%, range: 60.5-65.0%) and contrast-enhanced CT (64.4%, 61.5-67.8%). Non-contrast CT was non-inferior for the diagnosis of diverticulitis (accuracy 0.90 [95% confidence interval: 0.89, 0.92]) compared to contrast-enhanced CT (0.92 [0.90, 0.94]; the difference in accuracy: -0.01 [-0.04, 0.01]) (normal deviate test: p-value_one-sided = 5.20 × 10^-6). Sensitivities for perforation and abscess were slightly but significantly lower for the non-contrast CT than for the contrast-enhanced CT (differences: -0.15 [-0.20, -0.05], -0.17 [-0.27, -0.07]), while no differences in accuracies and specificities were observed. Conclusions: Non-contrast CT is non-inferior to contrast-enhanced CT (intravenous and rectal contrast) for the diagnosis of acute colonic diverticulitis. Contrast-enhanced CT is associated with significantly higher sensitivities for the presence of an abscess or perforation.

Keywords: colonic diverticulitis; computed tomography; contrast enema; non-contrast computed tomography; reader study.

Figure 1

Flowchart of the patient population.

Figure 2

Study design for readings and reference standards.

Figure 3

Bar chart showing the reader performance for diagnosing colonic diverticulitis in non-contrast and contrast-enhanced CT. The bars indicate accuracy, sensitivity, and specificity values for all readers (whiskers: 95% confidence intervals, CI). The lines indicate individual reader values: dark red and red (R1 and R2): board-certified radiologists; medium, dark, and light blue (R3, R4, R5): residents. Below the bars are the differences in accuracy, sensitivity, and specificity (with 95% CI). Note that the CIs of all differences shown include the 0.

Figure 4

Examples of diverticulitis cases without and with complications. Upper row: representative non-contrast CTs; bottom row: corresponding contrast-enhanced CT images. The number of accurate readings is given below each CT image. Left: In most cases, colonic diverticulitis was correctly diagnosed both in non-contrast and contrast-enhanced CT (arrow: thickened diverticulum with surrounding fat stranding). Middle left: Difficult case where diverticulitis was missed in non-contrast CT by the majority of readers (arrow: thickened segment of sigmoid colon with pericolic fat stranding). Middle right: The sensitivity for abscesses was slightly lower for non-contrast compared to contrast-enhanced CT (arrow: deep pelvic abscess). Right: Free peritoneal perforations were usually correctly diagnosed both in non-contrast and contrast-enhanced CT (arrow: free perihepatic air bubbles).