Abstract
Small bowel obstruction (SBO) is a common condition requiring urgent attention that may involve surgical treatment. Imaging is essential for the diagnosis and characterization of SBO because the clinical presentation and results of laboratory tests may be nonspecific. Ultrasound is an excellent initial imaging modality for assisting physicians in the rapid and accurate diagnosis of a variety of pathologies to expedite management. In the case of SBO diagnosis, ultrasound has an overall sensitivity of 92% (95% CI: 89–95%) and specificity of 93% (95% CI: 85–97%); the aim of this review is to examine the criteria for the diagnosis of SBO by ultrasound, which can be divided into diagnostic and staging criteria. The diagnostic criteria include the presence of dilated loops and abnormal peristalsis, while the staging criteria are represented by parietal and valvulae conniventes alterations and by the presence of free extraluminal fluid. Ultrasound has reasonably high accuracy compared to computed tomography (CT) scanning and may substantially decrease the time to diagnosis; moreover, ultrasound is also widely used in the monitoring and follow-up of patients undergoing conservative treatment, allowing the assessment of loop distension and the resumption of peristalsis.
Highlights
Small bowel obstruction is a common disease; its incidence in patients who present to the emergency department (ED) is estimated at 2–8%, and about 15% of these patients are admitted to the surgical unit [1,2,3]
The assessment of the intestinal loops is performed via the Global View technique [11,12]: a ‘global’ and panoramic assessment of the intestine is performed from the bottom upwards and with vertical probe movements exploring the entire abdomen starting from the right iliac fossa followed by horizontal movements from the right to the left side
At an early stage of the disease, the diameter should not be considered an absolute criterion for diagnosis, and other signs must be used: the bowel loop diameter at this stage could be within the normal range, but bowel loops are fluid-filled, hyperkinetic, and with plicar hyper-representation (Figures 1a and 2a) [12]
Summary
Simple mechanical ileus represents the first stage of occlusion, and it is characterized by the presence of a distended bowel upstream of the obstructive fulcrum, with gaseous or, more often, fluid/gaseous stasis; in this phase, the upstream loop shows hyper-kinesis and hyperrepresentation of valvulae conniventes This appearance reflects the bowel’s propulsive attempt to overcome the obstacle; the downstream loops instead present normal or reduced caliber. Complicated ileus represents a surgical emergency and is characterized by loop vascular distress with consequent vascular damage, necrosis, and subsequent bowel perforation with a high possibility of peritonitis and potentially fatal evolution In this stage, the upstream loops of the obstructive fulcrum are akinetic with parietal and valvulae conniventes thickening due to vascular infarction. This paper will review the diagnostic and staging signs of ultrasound in the diagnosis of small bowel obstruction
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