Varicose veins in the abdominal wall are usually caused by portal hypertension and vena cava occlusion. When portal hypertension is present, the direction of horizontal blood flow above the umbilicus is upward and below the umbilicus is downward. When the inferior vena cava is obstructed, the direction of blood flow is from bottom to top, and when the superior vena cava is obstructed, the direction of blood flow is from top to bottom. How to determine the direction of blood flow in the abdominal wall: Use the index and middle fingers together to compress a section of varicose vein that is not bifurcated, push the varicose vein that is not bifurcated toward both ends, and then alternately lift the index or middle finger to observe from which section the blood flows to fill the blood vessel, so that the direction of blood flow can be determined.