Microsclerotherapy is a therapy used to treat thread veins (also known as spider veins) on the legs. It is one of the most effective treatments available for the removal of thread veins. What does a Microsclerotherapy treatment involve? A very fine needle is used to inject a sclerosing agent directly into the thread vein. The sclerosing agent flows through the vein and stimulates the walls of the vein to swell up. The swelling prevents any blood to pass through the vessel and this causes the vein to shrivel up and disappear. Generally, patients will require two to three sessions for thread veins to be completely eradicated.