Classification Gastric outlet obstruction: only one/two air-fluid levels Homogeneous mass displacing transverse colon Duodenal obstruction: ■double-bubble sign; Frequently normal due to absence of gas from vomitingClassification ◼ Gastric outlet obstruction: ◼ only one/two air-fluid levels ◼ Homogeneous mass displacing transverse colon ◼ Duodenal obstruction: ◼ double-bubble sign; ◼ Frequently normal due to absence of gas from vomiting