Sclerotherapy is a treatment that intentionally damages the lining of veins by injecting a chemical, called a sclerosant, into the vein and inducing a chemical phlebitis or inflammation. By doing this and then applying pressure the vein walls stick together. The vein can then no longer fill with blood and so it is obliterated. The compression applied after the injection is an essential part of the therapy.
Ultrasound guided foam sclerotherapy (UGS) is a further development in which the foam injection is guided by ultrasound, and is used to treat smaller varicose veins. The ultrasound probe is able to track the needle entering the vein and ensure the injection takes place in the appropriate place. The dispersion of the foam can then be tracked using ultrasound. This is often used in combination with endovenous thermal ablation to give the best results.
Microinjection sclerotherapy is used for very fine spider veins and uses a very fine needle.