The normal direction of blood flow in the abdominal wall veins, above the umbilical level, flows from bottom to top through the chest wall veins and axillary veins into the superior vena cava and finally into the heart; below the umbilical level, it flows from top to bottom through the saphenous vein into the inferior vena cava and finally into the heart. Therefore, the direction of abdominal wall venous blood flow is different due to different obstructed vessels, mainly divided into the following categories: First, the superior vena cava is obstructed, affecting the parts above the umbilical level from bottom to top to top to bottom, while the direction of blood flow in the parts below the umbilical level remains unchanged, so the whole abdominal wall venous blood flow is from top to bottom. Second, inferior vena cava obstruction, which affects the parts below the umbilical level from up to down to down to up, and the parts above the umbilical level are not affected, so the whole abdominal wall venous blood flow is from down to up. Thirdly, portal vein obstruction, portal vein collects blood back to abdominal organs, after obstruction, the blood flow of abdominal wall vein flows in all directions with umbilicus as the center, also called jellyfish head, the blood flow direction is from bottom to top above umbilicus and from top to bottom below umbilicus.