Sclerotherapy is a procedure used to treat blood vessels or blood vessel malformations (vascular malformations) and also those of the lymphatic system. A medicine is injected into the vessels, which makes them shrink. It is used for children and young adults with vascular or lymphatic malformations. In adults, sclerotherapy is often used to treat varicose veins and hemorrhoids. 
Sclerotherapy is one method, along with surgery, radiofrequency and laser ablation, for treatment of varicose veins and venous malformations. In ultrasound-guided sclerotherapy , ultrasound is used to visualize the underlying vein so the physician can deliver and monitor the injection. Sclerotherapy should be done under ultrasound guidance after venous abnormailities have been diagnosed with duplex ultrasound. Sclerotherapy under ultrasound guidance and using microfoam sclerosants has been shown to be effective in controlling reflux from the sapheno-femoral and sapheno-popliteal junctions. However, some authors believe that sclerotherapy is not suitable for veins with reflux from the greater or lesser saphenous junction, or veins with axial reflux (above the knees).
Sclerotherapy has been used in the treatment of varicose veins for over 150 years. Like varicose vein surgery, sclerotherapy techniques have evolved during that time. Modern techniques including ultrasonographic guidance and foam sclerotherapy are the latest developments in this evolution.
Goldman says that the first reported attempt at sclerotherapy was by D Zollikofer in Switzerland, 1682 who injected an acid into a vein to induce thrombus formation. Both Debout and Cassaignaic reported success in treating varicose veins by injecting perchlorate of iron in 1853. Desgranges in 1854 cured 16 cases of varicose veins by injecting iodine and tannin into the veins. This was approximately 12 years after the probable advent of great saphenous vein stripping in 1844 by Madelung. The popularity of injection sclerotherapy increased over the late 19th century and early 20th century until the 1930s when several studies showed high recurrence rates. With the improvements in surgical techniques and anaesthetics over that time, stripping became the treatment of choice.
However work on improving the technique and development of safer more effective sclerosants continued through the 1940s and 1950s. Of particular importance was the development of sodium tetradecyl sulfate (STS) in 1946, a product still widely used to this day. George Fegan in the 1960s reported treating over 13,000 patients with sclerotherapy, significantly advancing the technique by focussing on fibrosis of the vein rather than thrombosis, concentrating on controlling significant points of reflux, and emphasizing the importance of compression of the treated leg. The procedure became medically accepted in mainland Europe during that time. However it was poorly understood or accepted in England or the United States, a situation that continues to this day amongst some sections of the medical community. 
The next major development in the evolution of sclerotherapy was the advent of duplex ultrasonography in the 1980s and its incorporation into the practise of sclerotherapy later that decade. Knight was an early advocate of this new procedure and presented it at several conferences in Europe and the United States. Thibault's article was the first on this topic to be published in a peer-reviewed journal.
The work of Cabrera and Monfreaux in utilising foam sclerotherapy along with Tessari's "3-way tap method" of foam production further revolutionised the treatment of larger varicose veins with sclerotherapy.
Injecting the unwanted veins with a sclerosing solution causes the target vein to immediately shrink, and then dissolve over a period of weeks as the body naturally absorbs the treated vein.
Sclerotherapy is the "gold standard" and is preferred over laser for eliminating large spider veins (telangiectasiae) and smaller varicose leg veins. Unlike a laser, the sclerosing solution additionally closes the "feeder veins" under the skin that are causing the spider veins to form, thereby making a recurrence of the spider veins in the treated area less likely. Multiple injections of dilute sclerosant are injected into the abnormal surface veins of the involved leg. The patient's leg is then compressed with either stockings or bandages that they wear usually for 2 weeks after treatment. Patients are also encouraged to walk regularly during that time. It is common practice for the patient to require at least 2 treatment sessions separated by several weeks to significantly improve the appearance of their leg veins.
Sclerotherapy can also be performed using microfoam sclerosants under ultrasound guidance to treat larger varicose veins, including the greater and short saphenous veins.
Foam sclerotherapy is a technique that involves injecting “foamed sclerosant drugs” within a blood vessel using a syringe. The sclerosant drugs (Sodium Tetradecyl Sulfate or polidocanol) are mixed with air or a physiological gas (carbon dioxide) in a syringe or by using mechanical pumps. This increases the surface area of the drug. The foam sclerosant drug is more efficacious than the liquid one in causing sclerosis (thickening of the vessel wall and sealing off the blood flow), for it does not mix with the blood in the vessel and in fact displaces it, thus avoiding dilution of the drug and causing maximal sclerosant action. It is therefore useful for longer and larger veins. Experts in foam sclerotherapy have created “tooth paste” like thick foam for their injections, which has revolutionized the non-surgical treatment of varicose veins  and venous malformations, including Klippel Trenaunay syndrome.
A study by Kanter and Thibault in 1996 reported a 76% success rate at 24 months in treating saphenofemoral junction and great saphenous vein incompetence with STS 3% solution. Padbury and Benveniste found that ultrasound guided sclerotherapy was effective in controlling reflux in the small saphenous vein.
A Cochrane Collaboration review of the medical literature concluded that "the evidence supports the current place of sclerotherapy in modern clinical practice, which is usually limited to treatment of recurrent varicose veins following surgery and thread veins."
A second Cochrane Collaboration review comparing surgery to sclerotherapy concluded that sclerotherapy has greater benefits than surgery in the short term but surgery has greater benefits in the longer term. Sclerotherapy was better than surgery in terms of treatment success, complication rate and cost at one year, but surgery was better after five years. However, the evidence was not of very good quality and more research is needed.
A Health Technology Assessment found that sclerotherapy provided less benefit than surgery, but is likely to provide a small benefit in varicose veins without reflux from the sapheno-femoral or sapheno-popliteal junctions. It did not study the relative benefits of surgery and sclerotherapy in varicose veins with junctional reflux.
The European Consensus Meeting on Foam Sclerotherapy in 2003 concluded that "Foam sclerotherapy allows a skilled practitioner to treat larger veins including saphenous trunks".
Complications, while rare, include venous thromboembolism, visual disturbances, allergic reaction, thrombophlebitis, skin necrosis, and hyperpigmentation.
If the sclerosant is injected properly into the vein, there is no damage to the surrounding skin, but if it is injected outside the vein, tissue necrosis and scarring can result. Skin necrosis occurs with 0.2% to 1.2% of sclerotherapy injections, is cosmetically "potentially devastating", often unpreventable, and may take months to heal. It is rare when small amounts of dilute (<0.25%) sodium tetradecyl sulfate (STS) is used, but has been seen when higher concentrations (3%) are used. Blanching of the skin often occurs when STS is injected into arterioles (small artery branches). Telangiectatic matting, or the development of tiny red vessels, is unpredictable and usually must be treated with repeat sclerotherapy or laser. .
A recent report attributed a stroke to foam treatment , although this involved the injection of an unusually large amount of foam.
- William R. Finkelmeier, Sclerotherapy, Ch. 12, ACS Surgery: Principles & Practice, 2004, WebMD (hardcover book)
- Kanter A, Thibault P. Saphenofemoral junction incompetence treated by ultrasound-guided sclerotherapy, Dermatol Surg. 1996. 22: 648-652.
- Padbury A, Benveniste G L, Foam echosclerotherapy of the small saphenous vein, Australian and New Zealand Journal of Phlebology Vol 8, Number 1 (Dec 2004)
- William R. Finkelmeier, Sclerotherapy, Ch. 12, ACS Surgery: Principles & Practice, 2004, WebMD (hardcover book)
- Goldman M, Sclerotherapy Treatment of varicose and telangiectatic leg vein, Hardcover Text, 2nd Ed, 1995
- Sharmi S, Cheatle T. Fegan's Compression Sclerotherapy of Varicose Veins, Hardcover Text, 2003.
- Knight R.M, Vin F, Zygmut J.A, Ultrasonic guidance of injection into the superficial venous system. Phlebologie '89 Davy A, Stemmer R (eds), 1989. John Libbey Eurotext Ltd pp. 339-341.
- Thibault P.K., Lewis W.A., recurrent varicose veins, Part 2: Injection of incompetent perforating veins using ultrasound guidance. J. Dermatol. Surg. Onc. 1992; 18: 895-900
- Cabrera Garrido Jr, Cabrera Garcia-Olmeda Jr,Garcia-Olmedo Dominguez MA. Elargissmen des limitz de la schleotherapie: Nouveaux produits sclerosants. Phlebologie:1997;50:181-188
- Monfreux A, Traitement sclerosant des trones saphen'nies et collaterales de gros calibre par le method MUS. Phlebologie 1997;50:351-353
- Tessari L. Nouvelle technique d'obtention de la sclero-mousse, Phlebologie 1997; 53:129
- Sadick N, Sorhaindo L, Laser Treatment of Telangiectatic and Reticular Veins, Ch 16, p157. The Vein Book / editor, John J. Bergan, 2007.
- Paul Thibault, Sclerotherapy and Ultrasound-Guided Sclerotherapy, The Vein Book / editor, John J. Bergan, 2007
- Yamaki T et al, Comparative study of duplex-guided foam sclerotherapy and duplex-guided liquid sclerotherapy for the treatment of superficial venous insufficiency. Dermatol Surg. 2004 May;30(5):718-22
- Alessandro Frullini MD, FACP, Attilio Cavezzi MD (2002) Sclerosing Foam in the Treatment of Varicose Veins and Telangiectases: History and Analysis of Safety and Complications. Dermatologic Surgery 28 (1), 11–15
- McDonagh, B, Sorenson, S et al. Management of venous malformations in Klippel–Trenaunay syndrome with ultrasound-guided foam sclerotherapy. Phlebology, Volume 20, Number 2, June 2005, pp. 63-81(19) 
- Tisi PV, Beverley C, Rees A. Injection sclerotherapy for varicose veins. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD001732. 
- Rigby KA, Palfreyman SJ, Beverley C, Michaels JA. Surgery versus sclerotherapy for the treatment of varicose veins. Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD004980. 
- Michaels JA, Campbell WB, Brazier JE, MacIntyre JB, Palfreyman SJ, Ratcliffe J, et al. Randomized clinical trial, observational study and assessment of cost-effectiveness of the treatment of varicose veins (REACTIV trial). Health Technol Assess 2006;10(13).  This Health Technology Assessment monograph includes reviews of the epidemiology, assessment, and treatment of varicose veins, as well as a study on clinical and cost effectiveness of surgery and sclerotherapy
- Franz-Xaver Breu, Stephan Guggenbichler (2004)European Consensus Meeting on Foam Sclerotherapy, April, 4-6, 2003, Tegernsee, Germany Dermatologic Surgery 30 (5), 709–717.
- Bruce Campbell, Varicose veins and their management, BMJ, 2006;333:287-92
-  Medscape. William R. Finkelmeier, What's New in ACS Surgery: Sclerotherapy. ACS Surgery 2003. [free signup required]
- Forlee, MV et al., Stroke after varicose vein foam injection sclerotherapy, J Vasc Surg 2006;43:162-4
- Ultrasound Guided Sclerotherapy http://youtube.com/watch?v=Lkl6btffR0A
- Management of venous malformations in Klippel–Trenaunay syndrome with ultrasound-guided foam sclerotherapy
- Information about Lymphatic Malformations and the use of sclerotherapy to treat them from Children's Hospital, Seattle
- Ultrasound video of a sclerotherapy taking place