Portal hypertension can result in dilated abdominal veins surrounding the umbilicus (caput medusa).
Normally abdominal veins are invisible or barely visible. Loss of abdominal wall fat or increased pressure in the superior vena cava (SVC), inferior vena cava (IVC), or portal vein can make the vessels visible, particularly in the red or infrared spectrum.
The normal direction of blood flow in abdominal veins is upward above the umbilicus, and downward below the umbilicus. In portal hypertension the direction of flow is normal; in SVC obstruction, the flow is all downward; and in IVC obstruction the flow is all upward.