A simple obstruction is blocked in one place; a closed-loop obstruction is blocked in two places.

A closed-loop obstruction may develop when the bowel twists around on itself, isolating the looped section of the bowel and obstructing the portion above it.

However improvements in radiologic imaging of small bowel obstructions allow for confident distinction between simple obstructions, that can be treated conservatively, and obstructions that are surgical emergencies (volvulus, closed-loop obstructions, ischemic bowel, incarcerated hernias, etc.).