Small bowel obstruction: follow the to-and-fro

Answer c. Small bowel wider than 2.5 cm, measured from outer wall to outer wall, counts as dilated. A diameter over about 3 cm is commonly used too, so some guides quote 2.5 to 3 cm. Measure the widest loop you find.

Answer d. Strong peristalsis against a blockage pushes contents forward, and they fall back, giving to-and-fro movement. In ileus, peristalsis is weak or absent throughout. Normal peristalsis moves contents in one direction.

Answer a. The transition point is where dilated bowel above the blockage meets collapsed bowel beyond it. Follow dilated loops in a systematic sweep until they change calibre. The largest loop is not necessarily next to the blockage.

Answer b. As obstruction progresses, the bowel tires and peristalsis fades, so a late mechanical obstruction looks like ileus. Use the history, the examination and CT to define the cause. Delay risks missing strangulation.

Answer d. Free fluid between loops, a thick bowel wall and loss of peristalsis suggest compromised bowel. These patients need urgent surgical review and CT. Valvulae conniventes identify small bowel. To-and-fro movement and modest dilatation are features of obstruction itself.