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Multidetector CT for GI bleeding: first-line diagnostic study?

Acute gastrointestinal (GI) bleeding represents a common medical emergency with severe potential clinical consequences. With an annual incidence of 40 to 150 episodes per 100,000 persons for upper GI bleeding, and 20 to 27 episodes per 100,000 persons for lower GI bleeding in the United States, this diagnosis is seen fairly frequently across the spectrum of all clinical practices. At the same time, the morbidity and mortality for this diagnosis remain high, with almost 300,000 hospital admissions every year, and death rates approaching 40% for patients with hemodynamic instability. Given its high clinical impact, early diagnosis and treatment remain a goal of all clinicians who need to manage this disease. Unfortunately, current diagnostic algorithms vary widely from institution to institution and from clinician to clinician. Imaging modalities remain the mainstay of the diagnostic approach. They include endoscopy, videocapsule, radionuclide imaging, catheter angiography, and multidetector computed tomography (MDCT) imaging. For years, endoscopy has been the initial standard approach to patients who present with acute GI bleeding. Endoscopy represents a safe and effective method to diagnose and often treat GI bleeding in a controlled environment. The sensitivity and specificity of endoscopy for upper GI bleeding are very high, approaching 98% and 100%, respectively. However, while esophagogastroduodenoscopy clearly is a first-line tool for diagnosis and treatment of upper GI bleeding, colonoscopy remains challenging for lower GI bleeding, with the ability to identify a definite bleeding source in only 13% of patients. The necessity of adequate bowel preparation precludes the ability of colonoscopy to be utilized effectively in urgent clinical situations. Overall, conventional endoscopy suffers from an inability to directly visualize the distal duodenum and small bowel. Videocapsule represents a promising tool to overcome these anatomic areas, but it is inappropriate in the emergent setting. Traditionally, radionuclide imaging with technetium 99m-labeled red blood cells has been utilized as an adjunct tool to evaluate lower GI bleeding, and has been shown to detect active bleeding at a rate of 0.2mL/min. The noninvasive nature of this modality and lack of necessary patient preparation are advantageous for many clinicians. However, the availability of nuclear medicine may be limited at some institutions in an overnight emergency room setting. In addition, the lack of accurate anatomic detail obtained by nuclear imaging may make subsequent intervention a challenge. Catheter angiography has proven to be a useful tool in both the diagnosis and treatment of GI bleeding. Experimental studies in dogs have established its ability to diagnose bleeding rates from 0.5 to 1.0mL/s. In addition, catheter angiography offers the possibility of immediate treatment through embolization of active bleeding sites or through infusion of vasopressin, thereby saving the cost and time of subsequent interventions. However, angiography is often operator dependent, and represents an invasive tool that may not be appropriate for every patient. In recent years, MDCT has emerged as a promising technology to evaluate GI bleeding. The modality’s ubiquitous nature, ease of use, and rapid results favor its use in any emergent situation. In addition, today’s high-speed, narrow collimation multidetector technology allows a large coverage area with minimal motion artifacts, with the ability to capture both arterial and venous phase with ease. Swine models have shown that MDCT can capture bleeding rates as low as 0.4mL/min. Despite the theoretical promise of MDCT in a challenging clinical situation, published reports have been limited as to its true clinical effectiveness. Hara et al retrospectively reviewed 48 patients with suspected GI hemorrhage, and found that MDCTdetected GI bleeding with an overall sensitivity and specificity of 33% and 89%, respectively. Interestingly, in subgroup analysis, first time GI bleeding had an improved sensitivity and specificity of 42% and 100%, with a sharp decline in effectiveness in obscure GI bleeding, with sensitivity and specificity rates of 22% and 85%. In a recent article, Huprich et al