Classification location ■ 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 - location ◼ 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