Multidetector CT Angiography for the Detection of Colonic Diverticular Bleeding: When, How, and Why?

Abstract

Acute lower GI bleeding is responsible for 1–2 % of hospital emergencies, 15 % of which manifest as massive, lifethreatening bleeding. Initial clinical management focuses on identifying the site and cause of bleeding using scintigraphy, arteriography, and colonoscopy [1–3]. Although optical colonoscopy is the procedure of choice, its use poses challenges in the emergency setting [1]. Administration of bowel preparation, not always feasible in cases of massive bleeding, can delay the procedure for several hours; the presence of clots, blood, and stool in patients without preparation may hinder the visualization of the bleeding point, increasing the rate of incomplete studies when compared with nonemergent examinations. Furthermore, in 10–12 % of cases, the source of bleeding may be extracolonic [4]. Angiography is an invasive procedure usually reserved for therapeutic purposes in patients with more severe, life-threatening bleeding. Technetium 99labeled red blood cell scintigraphy is more sensitive than arteriography for identifying lower rate bleeding, although its emergency availability is variable, limiting its usefulness [4]. Computed tomography (CT) and, more specifically, CT enterography is commonly used as a second-line procedure in nonemergent patients with unexplained GI bleeding after negative upper and lower endoscopy examinations [5]. Since CT is rapid, noninvasive, and highly reproducible, it is commonly used in the acute setting for evaluating patients with lower GI bleeding emergencies, although optimal timing and patient characteristics for the diagnosis of colonic diverticular bleeding have not been established. In this issue, Obana et al. [6] prospectively explored the utility of contrast-enhanced CT in 52 patients with colonic diverticular bleeding testing the hypothesis that CT complements colonoscopy in this setting. Favorable patient characteristics, based on univariate analysis, included feasibility of examination within 2 h of the last hematochezia, re-bleeding in hospital, or past history of diverticular bleeding. Detection and localization of the bleeding source enable successful catheter-directed endovascular therapy. Although emergent colonoscopy remains the primary investigation in lower GI bleeding, it is often negative or impractical during the acute phase in hemodynamically unstable patients, as confirmed in the accompanying study [6]. In many centers, CT angiography is performed if endoscopy fails to identify the bleeding source with conventional mesenteric angiography reserved for patients with CT evidence of active contrast extravasatio or hemodynamic instability due to massive hemorrhage. CT may visualize acute lower GI bleeding at a bleeding rate less than the 0.5 ml/min limit cited for mesenteric angiography, perhaps as low as 0.2 ml/min [5]. The additional information provided by CT before attempted therapeutic angiographic procedures improves the preoperative localization and characterization of the bleeding source, expediting the selective catheterization of bleeding vessels, thereby significantly facilitating embolization. Relevant findings evaluated in this study were the presence and location of active or recent bleeding and the identification of the potential bleeding lesion [6]. Active bleeding from colonic diverticula was identified in only 15.4 % (8/52) of the patients included in the study, lower than in other series that included only massive or severe bleeding, probably because most patients were hemodynamically stable at the time CT was performed. In many R. Loffroy (&) Department of Vascular and Interventional Radiology, Bocage Teaching Hospital, University of Burgundy School of Medicine, Dijon, France e-mail: romaric.loffroy@chu-dijon.fr