Ultrasound has better sensitivity and specificity than a plain x-ray for the diagnosis of small bowel obstruction. One metanalysis looked at x-ray, CT, MRI, and US for diagnosis of SBO. SBO was diagnosed if there were >2.5cm loops of small bowel proximal to collapsed bowel segments, and/or with absent or decreased peristaltic activity (defined as to and fro peristalsis). Two Studies looked at bedside ultrasound by emergency physicians in particular. Sensitivity and specificity were 97 and 90% respectively with likelihood ratios of positive 9.5 and negative of 0.04, better than both CT and MRI as well.1,2 Keyboard sign, or visualization of the plicae circularis clearly, and to and fro peristalsis are other features of SBO.3
