How does ethanol ablation work?

Fluid filled thyroid cysts have a thin wall which are lined by cells (epithelial cells). These epithelial cells produce the fluid. This means simply aspirating the fluid content of a cyst is very often ineffective as the cells quickly replace the fluid that has been removed. Injection of ethanol after aspiration chemically injures the epithelial cell wall. This causes inflammation and eventually scarring which inactivates and prevents the cells from producing further fluid. In this way the nodule shrinks.