Objective We evaluated the diagnostic performance of computed tomography (CT) as an initial radiologic test for assessing the optimal timing of colonoscopy in patients with acute lower gastrointestinal bleeding (LGIB) and investigated the effectiveness of contrast-enhanced (CE) CT for detecting colonic diverticular bleeding. Methods This was a retrospective study of 1,604 consecutive patients who visited or were referred to St. Marianna University Hospital due to acute LGIB and underwent colonoscopy within three months after presentation between September 2004 and December 2012. The clinicopathological data of the subjects were obtained from their medical records. Results Among the 1,604 patients presenting with LGIB, 879 (55%) underwent a CT scan. Elective colonoscopy was considered in cases in which typical colonic wall thickening was observed on CT, suggesting colonic inflammation or malignancy (239 patients; 27%). The diagnoses in the elective cases included ischemic colitis (38%), infectious colitis (8%), inflammatory bowel disease (8%) and malignancy (5%). Urgent colonoscopy was performed after the CT examination in 640 cases (73%). The most common presumptive CT diagnosis was diverticulum (402/640; 63%). Of the 638 patients who underwent CE-CT, diverticula were observed in 346 cases, including 104 cases of extravasation indicating ongoing diverticular bleeding. Among these 104 patients, the site of bleeding was identified in 71 subjects (68%) during colonoscopy. The rate of detection of the bleeding source on colonoscopy was significantly higher in the patients with extravasation on CE-CT than in those without extravasation on CE-CT (68% vs. 20%, respectively; p<0.001). Conclusion Urgent CT is useful for determining the optimal timing of colonoscopy in cases of acute LGIB. CE-CT may be used to depict the presence and location of active hemorrhage and provides useful information for subsequent colonoscopy, especially in patients with diverticular bleeding.
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