Sclerotherapy is a medical procedure used to treat abnormal blood vessels, arteriovenous malformations, and lymphatic system malformations. It involves the injection of drugs which shrink and close the vessels in question, which then permanently close and dissolve back into the body. For larger blood vessels, the injection can be guided by ultrasound. In addition to being used to treat malformations, it is used to treat spider veins, small varicose veins and hemorrhoids. It is minimally invasive and has a success rate similar to surgery without the need for a lengthy recovery time.