Spider nevus is a vascular dilatation that resembles a spider. It is an idiopathic hairy vasodilatation, which is formed by the dilatation of the ends of small arterial branches in the skin. Spider nevus has a red spot in the center, surrounded by a radial pattern of small blood vessel branches, very similar to a red spider, so it is named spider nevus. Spider nevus tends to occur in areas where the superior vena cava is distributed, such as the face, neck, upper chest, shoulders and upper limbs. Clinically, it can be seen in cirrhosis, acute hepatitis and chronic liver disease, and also in healthy people such as children and pregnant women. There are many causes of spider nevus, but it is now thought to be related to high estrogen levels and not necessarily caused entirely by cirrhosis, so spider nevus is a dilated blood vessel with a spider-like morphology.