In large bowel obstruction the dilated loops are peripheral with haustra, there is no air in the rectum, and the caecum distends most (thresholds: >9-10 cm for caecum/right colon vs >6 cm for the left colon). Central dilated loops (A) suggest small bowel obstruction, and gas in the rectum (C) argues against a complete obstruction. Hypoechoic loops on ultrasound (B) is not a described feature.