Imaging description

Bowel obstruction is the partial or complete blockage of the small or large intestine, while strangulated bowel obstruction is intestinal blockage accompanied by compromised blood flow. Non-strangulated or simple bowel obstruction is often successfully managed conservatively, while strangulated obstruction is a surgical emergency which can progress to infarction and gangrene in as little as six hours. Strangulation is usually associated with hernias (including internal hernias) or volvulus. In two large surgical series, strangulation occurred in 17 to 23% of small bowel obstructions [1,2], but it should be remembered that many simple obstructions do not require surgery and so the true frequency of strangulation in “all-comers” with bowel obstruction is likely to be considerably lower. Irrespective of the presence or absence of strangulation, the cardinal imaging sign of obstruction is the finding of dilated bowel upstream to collapsed or non-dilated bowel. CT can usually detect the transition point between dilated and non-dilated bowel and suggest the likely etiology (such as hernia, mass, or intussusception – the lack of a visible cause suggests adhesions). The supplementary CT features that indicate strangulation are reduced bowel wall enhancement, mural thickening, mesenteric fluid or infiltration, congestion of small mesenteric veins, ascites, pneumatosis, and portal venous gas (Figures 56.1 and 56.2) [1–5]. The described supplementary CT signs of strangulated internal hernia are clustering of disproportionately dilated bowel segments, swirling or convergence of mesenteric vessels, and mesenteric vessel engorgement (Figure 56.3) [6, 7].