Last updated: 11/24/2009

Causes of spider veins

To understand how sclerotherapy works, it is helpful to begin with a brief description of the venous system in the human body. The venous part of the circulatory system returns blood to the heart to be pumped to...

the lungs for oxygenation. This is in contrast to the arterial system, which carries oxygenated blood away from the heart to be distributed throughout the body. The smallest parts of the venous system are the capillaries, which feed into larger superficial veins. All superficial veins lie between the skin and a layer of fibrous connective tissue called fascia, which covers and supports the muscles and the internal organs. The deeper veins of the body lie within the muscle fascia. This distinction helps to explain why superficial veins can be treated by sclerotherapy without damage to the larger veins.

Veins contain one-way valves that push blood inward and upward toward the heart when they are functioning normally. The blood pressure in the superficial veins is usually low, but if it rises and remains at a higher level over a period of time, the valves in the veins begin to fail and the veins dilate, or expand. Veins that are not functioning properly are said to be "incompetent." As the veins expand, they become more noticeable because they lie closer to the surface of the skin, forming the typical patterns seen in spider veins.

Some people are at greater risk for developing spider veins. These risk factors include:

• Sex. Females in any age group are more likely than males to develop spider veins.
• Genetic factors. Some people have veins with abnormally weak walls or valves. They may develop spider veins even without a rise in blood pressure in the superficial veins.
• Pregnancy. A woman's total blood volume increases during pregnancy, which increases the blood pressure in the venous system. In addition, the hormonal changes of pregnancy cause the walls and valves in the veins to soften.
• Using birth control pills.
• Obesity. Excess body weight increases pressure on the veins.
• Occupational factors. People whose jobs require standing or sitting for long periods of time without the opportunity to walk or move around are more likely to develop spider veins than people whose jobs allow more movement.

• Trauma. Falls, deep bruises, cuts, or surgical incisions may lead to the formation of spider veins in or near the affected area.

As of 2003, there is no known method to prevent the formation of spider veins.

Sclerotherapy procedures

In typical outpatient sclerotherapy treatment, the patient changes into a pair of shorts at the doctor's office and lies on an examination table. After cleansing the skin surface with an antiseptic, the doctor injects a sclerosing agent into the veins. This agent is eliminated when the skin is stretched tightly over the area with the other hand. The doctor first injects the larger veins in each area of the leg, then the smaller ones. In most cases, one injection is needed for every inch of spider vein; a typical treatment session will require five to 40 separate injections. No anesthetic is needed for sclerotherapy, although the patient may feel a mild stinging or burning sensation at the injection site.

The liquid sclerosing agents that are used most often to treat spider veins are polidocanol (aethoxysklerol), sodium tetradecyl sulfate, and saline solution at 11.7% concentration. Some practitioners prefer to use saline because it does not cause allergic reactions. The usual practice is to use the lowest concentration of the chemical that is still effective in closing the veins.

A newer type of sclerosing agent is a foam instead of a liquid chemical that is injected into the veins. The foam has several advantages: It makes better contact with the wall of the vein than a liquid sclerosing agent; it allows the use of smaller amounts of chemical; and its movement in the vein can be monitored on an ultrasound screen. Sclerosing foam has been shown to have a high success rate with a lower cost, and causes fewer major complications.

After all the veins in a specific area of the leg have been injected, the doctor covers the area with a cotton ball or pad and compression tape. The patient may be asked to wait in the office for 20–30 minutes after the first treatment session to ensure that there is no hypersensitivity to the sclerosing chemicals. Most sclerotherapy treatment sessions are short, lasting from 15 to 45 minutes.

It is not unusual for patients to need a second treatment to completely eliminate the spider veins; however, it is necessary to wait four to six weeks between procedures.