Thermal vein closure

This effect is a pathophysiological mechanism, not a technique. It describes what happens in the vein wall under the action of heat. Several venous ablation modalities exploit it, by different routes. HIFU treatment achieves it without introducing any heat source into the vessel.

The mechanism

The vein wall is rich in collagen, the structural protein that gives it its hold. Under a rise in temperature, this collagen denatures: its structure unfolds, the fibers contract. The wall retracts, its lumen closes.

This occlusion interrupts the reflux that fed the varicose dilation. The treated segment, deprived of flow, is then resorbed by the body. This mechanism is thermal. Heat is its sole agent: it leads to a coagulation of the wall through a rise in temperature, not to a mechanical rupture of the vessel.

This mechanism was characterized by numerical modeling of energy deposition and wall retraction, then verified by animal studies before any clinical use.

The temperature threshold

The intended effect depends on the temperature reached in the wall. In HIFU treatment, the beam converges at a millimeter-sized focal point, where acoustic absorption produces rapid, strictly localized heating. The temperature there reaches up to 90°C.

This value is that of the focal point. Outside this small volume, energy density stays low and the heating does not become damaging. The geometry of the beam thus confines the thermal effect to the target, while a cooling system protects the skin during the pulses.

Without intravascular contact

Thermal ablation modalities produce the same biological effect on the wall, collagen denaturation followed by retraction. They part ways on where the heat is applied.

Laser and radiofrequency introduce a heat source into the vein, reached by catheter. HIFU treatment delivers the energy from the outside, without contact with the inner wall. This difference carries a practical consequence: an intravascular source requires protecting neighboring tissue with tumescent anesthesia, a fluid sleeve injected around the vein. A focused extracorporeal source shifts that constraint toward control of the beam and cooling of the skin.

What thermal closure does not cover

Thermal closure describes a mechanism, not an efficacy. The fact that a technique closes the vein with heat prejudges neither its occlusion rate nor its safety, dimensions that depend on clinical data specific to each modality.

This mechanism also does not cover the non-thermal venous ablation techniques, such as cyanoacrylate glue or mechanochemical ablation, which close the vein without a rise in temperature. Venous HIFU treatment, for its part, does fall under the thermal mechanism, to be distinguished from non-thermal uses of ultrasound developed by other players and not covered by this definition.