Besides perforated appendicitis and intussusception, the most common causes of small bowel obstruction are incarcerated hernias and adhesions. Other causes of small bowel obstruction comprise a miscellaneous group of rare conditions, such as midgut volvulus, Meckel's diverticulum, advanced stages of Crohn's disease, and bezoars. Adhesions usually result from prior surgery and are often multiple. There is an increasing tendency for initial conservative management rather than immediate operative intervention, as a proportion of cases will resolve spontaneously.
The diagnosis of bowel obstruction is established on clinical grounds and usually confirmed with plain abdominal radiographs. Plain radiographs usually show distended bowel loops with air-fluid levels (Fig. 1.66). In inguinal incarcerated hernia, plain film will also show thickening of the right inguinoscrotal fold (Fig. 1.67a). Because of the diagnostic limitations of plain films, cross-sectional methods are increasingly used. At US, dilated, fluid-filled small bowel loops are seen, which are recognized by the presence of the valvu-lae conniventes. The bowel wall may become edem-atous due to vascular and lymphatic obstruction, and ascites may be an accompanying feature of intestinal obstruction. In patients with mechanical bowel obstruction, hyperperistalsis with a to-and-fro motion of the bowel contents is often observed during real-time imaging. Once the obstruction becomes high-grade or complete, peristalsis may be absent (O'Malley and Wilson 2003). Peristals-ing fluid and air-filled loops of bowel or mesenteric fat passing down the canal into the scrotum can be readily identified in inguinal hernias (Fig. 1.67b). At US or CT a diagnosis of adhesion is assumed when there is no identifiable lesion at the transition zone between the dilated and the collapsed bowel loops, because the adhesive band itself is not visualized (Marincek 2002).
Closed loop obstruction is a form of mechanical bowel obstruction in which two points along the course of the bowel are obstructed at a single
Fig. 1.67a-c. Incarcerated right inguinal hernia. a Plain film shows dilated loops of small bowel and thickening of the right inguinoscrotal fold (arrowhead). b US scan shows dilated small bowel loops and ascites. Note the typical appearance of the bowel wall with five layers (arrow). c Longitudinal US of the right inguinoscrotal fold performed with an interposed gel-pad, shows an air-filled loop (arrows) passing down the canal into the scrotum. The scrotum shows a normal appearance. Normal testis (T) and fluid. A, ascites
Fig. 1.67a-c. Incarcerated right inguinal hernia. a Plain film shows dilated loops of small bowel and thickening of the right inguinoscrotal fold (arrowhead). b US scan shows dilated small bowel loops and ascites. Note the typical appearance of the bowel wall with five layers (arrow). c Longitudinal US of the right inguinoscrotal fold performed with an interposed gel-pad, shows an air-filled loop (arrows) passing down the canal into the scrotum. The scrotum shows a normal appearance. Normal testis (T) and fluid. A, ascites site. It is usually secondary to an adhesive band or a hernia. Because a closed loop tends to involve the mesentery and is prone to produce a volvulus, it represents the most common cause of strangulation. Characteristic findings of closed-loop obstructions are a C-shaped, U-shaped, or "coffee bean" configuration of the bowel loop (Marinoek 2002) (Fig. 1.68). Mechanical obstruction of the gut must be differentiated from paralytic ileus. Numerous causes exist for both diffuse and localized paralytic ileus and gaseous distention of the small and the large intestine are seen. Paralytic ileus is a common problem after abdominal surgery. It may be secondary to inflammatory or infectious disease, abnormal electrolyte, metabolite, drug or hormonal level, or innervation defects. Plain radiographs show diffuse dilated bowel loops with distal air, as well as air-fluid levels in the upright or decubitus radiograph (Marincek 2002) (Fig. 1.69). Differentiation of paralytic vs mechanical ileus can also be documented by M-mode US (Riccabona 2001).
Fig. 1.68a-d. Ileal adhesions from previous appendicectomy causing small bowel obstruction. Supine (a) and upright (b) plain abdominal radiographs show a paucity of abdominal air and a few air-fluid levels indicating small bowel obstruction indistinguishable from any other cause of obstruction. c,d Sonography at the right and left lower quadrants demonstrate a U-shaped, or "coffee bean", configuration of the dilated bowel loops (arrows). Some bowel loops present a thickened wall (arrowhead) and ascites (A), suggesting strangulation a c
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