Role of MDCT in Diagnosis of Small Bowel Obstruction

Abstract

Since the early 1990s, the management of small bowel obstruction has dramatically changed. No longer does the dictum ‘‘never let the sun set on a small bowel obstruction’’ hold true. Currently, patients without evidence of strangulation are treated conservatively with nasogastric decompression. As many of the other causes of acute abdomen are treated surgically, identification of SBO is critical to reduce morbidity and mortality due to unnecessary surgery(Kohli&Maglinte, 2009; Seror et al., 1993). The clinical diagnosis of SBO classically depends on four cardinal findings: abdominal pain, vomiting, constipation and abdominal distension. Conventional abdominal radiography is the preferred initial radiologic examination. It is usually obtained initially and has overall 69%, 57%, and 67% sensitivity, specificity, and accuracy, respectively, for the diagnosis of obstruction(Birnbaum, 2001; Herlinger&Rubesin 1994; Maglinte et al., 1997). The diagnosis is often not straightforward and frequently not established on the basis of clinical and radiographic findings. Moreover, closed loop and strangulated obstructions (true surgical emergencies) are not easily diagnosed clinically (Macari&Megibow, 2001). The pattern of major causes of SBO has changed over the past five decades. The most common cause was originally external hernia. Now, adhesions compose 60–80% of the total number of SBOs in industrialized countries. The prevalence of the different causes of SBO varies according to the clinical context (Taourel et al., 2011). The development in computed tomography (CT) from single-detector to multidetector equipment has overcome peristaltic intestinal artifacts, allowing optimal bowel visualisation and contrast enhancement (CE). As a result, this permits a finer representation and a more accurate evaluation of the bowel and mesentery. Furthermore, technological advances now allow high-quality reformatted series particularly coronal reformatting useful in the identification of the transition point and in the analysis of the cause and of the mechanism of the obstruction.To date, contrast enhanced MDCT has become the gold standard in the evaluation of small bowel obstruction (SBO)and differentiating it from ileus, in identifying the transition point,in locating the site of the obstruction, in determining the cause of the obstruction, which may be intraluminal, intrinsic or extrinsic and finally in looking for a complication such as closed loop obstruction or ischemia(Di Mizio et al., 2007; Taourel et al., 2011). CT determines the site of SBO by detecting the site of the transition zone and by surveying all the abdominal axial images and comparing the relative lengths of the prestenotic versus collapsed intestine. The diagnosis of the severity of the obstruction theoretically needs use of oral contrast material. However, in clinical practice, oral contrast material is generally not given. Therefore, the severity of the obstruction is deter- mined by the degree of collapse and the amount of residual contents in the portion of the bowel distal to the obstructed site (Taourel et al., 2011). In patients with suspected intestinal obstruction, the primary diagnostic triage is based on clinical, laboratory and abdominal plain film findings. If a strong suspicion of SBO and if there are findings of strangulation or the cause of the SBO is obvious and needs emergent surgical management, surgery must be performed without other investigations. In other patients with acute symptoms, CT helps in the search for the mechanism and cause. In patients with non-acute symptoms (suspicion of low-grade obstruction), CTenteroclysis is a good alternative to CT. If there is a strong suspicion of paralytic ileus, the cause must be investigated by clinical and laboratory examinations and in some cases by ultrasonography or CT(Taourel et al., 2011). Computed tomography enteroclysis is an excellent and proven diagnostic modality for evaluating small bowel pathology. This fused test combines the advantages of enteral challenge from a catheter small-bowel examination (enteroclysis) with the isotropic, multiplanar, cross-sectional images obtained at CT. The diagnostic yield of CT enteroclysis in patients with low-grade small bowel obstruction is much better than conventional CT, with a sensitivity and specificity of 89% and 100%, respectively(Gollub, 2009; Lalitha et al., 2011; Sailer et al., 2005).