Telangiectasia or spider veins are small dilated blood vessels that appear on the surface of the skin or in the mucous membranes.  They can be distinguished from other similar conditions by the fact that they become much lighter in color when pressure is applied to them.  

Telangiectasia can be caused by numerous congenital and acquired conditions.  They can be benign or can indicate an underlying condition.  Some of the causes of telangiectasia are birthmarkshereditary hemorrhagic telangiectasiaCushing's syndromevaricose veinsacneradiation therapy and chemotherapy.

In most cases, no matter what the cause, telangiectasia can be treated by sclerotherapy, a process which hardens the veins so they eventually close off.  However, sclerotherapy is contraindicated if the patient also has large dilated veins, in which case it can lead to deep-vein thrombosis.  

Telangiectasia at Wikipedia

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