A spider angioma (also known as a nevus araneus, spider nevus, or vascular spider) is a type of angioma found slightly below the skin's surface, often containing a central red spot and reddish extensions which radiate outwards like a spider's web. They are common and benign, present in around 10-15% of healthy adults and young children.
Spider angiomas are commonly found on the face, neck, upper part of the trunk and arms. They may also be present on the backs of the hands and fingers in young children. Most, however, are a result of liver disease. They are due to failure of the sphincteric muscle surrounding a cutaneous arteriole. The central red dot is the dilated arteriole and the red "spider legs" are small veins carrying away the freely-flowing blood. If momentary pressure is applied, it is possible to see the emptied veins refilling from the centre. No other angiomas show this phenomenon.
Many pregnant women, or women using hormonal contraception, have spider angiomas, due to high estrogen levels in their blood. People who have significant hepatic disease also show many spider angiomas, as their liver cannot detoxify estrogen from the blood, resulting in high levels of estrogen. About 33% of patients with cirrhosis have spider angiomas. As such, microhemorrhages may be observed as spider angiomas.
Spider angiomas are asymptomatic and usually resolve spontaneously. This is common in the case of children, although they may take several years to disappear. If the spider angiomas are associated with pregnancy, they may resolve after childbirth. In women taking oral contraceptives, they may resolve after stopping these contraceptives. The spider angiomas associated with liver disease may resolve when liver function increases or when a liver transplant is performed.
For spider angiomas on the face, techniques such as electrodesiccation and laser treatment can be used to remove the lesion. There is a small risk of a scar, although the results are generally good. Spider angiomas can recur after treatment.
If the centre of the angioma is pricked with a hypodermic needle, opening the dilated arteriole, blood will flow freely for some time unless pressure is applied; the arteriole will then shrink or coagulate and the angioma will disappear. This treatment is minimally painful and leaves no scar.