The stomach is located mainly in the left upper quadrant beneath the diaphragm and is attached superiorly to the esophagus and distally to the duodenum. The stomach is divided into four portions: cardia, body, antrum, and pylorus. Inflammation, scarring, or infiltration of the antrum and pylorus are associated with the development of GOO.
The duodenum begins immediately beyond the pylorus and mostly is a retroperitoneal structure, wrapping around the head of the pancreas. The duodenum classically is divided into four portions. It is intimately related to the gallbladder, liver, and pancreas; therefore, a malignant process of any adjacent structure may cause outlet obstruction due to extrinsic compression