- Trans-isthmus approach - Remove all fluid - Put back 50% of aspirated fluid in the form of 95-99% ethanol - Let sit for 2 mins - Can aspirate it all or leave it in - Don't leave more than 10 mL of ethanol https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6424836/ The patient is placed in a supine position on the bed with mild neck extension. After skin sterilization, local anesthetic (1–2% lidocaine) is usually injected at the skin puncture site. Depending on the viscosity of the contents in the cyst, a single 16–20 G needle is inserted into the center of the cystic area under US guidance. A trans-isthmic approach route is recommended to prevent a change in the position of the needle tip and ethanol leakage when the patient swallows or talks (Fig. 1). As much internal fluid is aspirated as possible and residual debris or colloids are removed by saline irrigation. High viscosity fluid of colloid cysts may be difficult to aspirate. Several studies on the evacuation of viscous cystic thyroid nodules have used normal saline irrigation to decrease viscosity, repeated ethanol injection into the nodules with an interval period, a large-bore needle, or even a large pigtail catheter connected to a suction pump (89,90,91,92,93). Then, the operator slowly injects an appropriate amount of 95–99% ethanol into the cystic space. The amount of ethanol injected depends on the amount of aspirated material in the nodule; approximately 50% of the aspirate volume is usually injected. Total retention amount of ethanol is empirically recommended not to exceed 10 mL, even for large-sized nodules (19,28,51,56,94). However, if injected ethanol is to be removed after the procedure, a larger amount of ethanol can be used. A sufficient consensus has not yet been established regarding the total amount of ethanol to use for injection. The exact ethanol amount should be tailored according to the size and internal content of the lesion, the opinion of the operator during the procedure, and patient compliance. An ethanol retention time of 2 minutes was found to be sufficient by Kim et al. (95), because ethanol reacts rapidly with cells. However, there is no consensus on whether ethanol should be re-aspirated or not after the procedure. Several studies have suggested that a short retention (at least 2 minutes) and complete removal of ethanol is preferable because longer ethanol retention times may increase patient inconvenience and complications due to possible leakage of ethanol (95,96). This also has the advantage that the patient's satisfaction is high, because the size of the nodule is reduced immediately after the procedure. Kim et al. (53) reported that there was no difference in complication or success rated between groups in which ethanol was not aspirated or aspirated after injection. Therefore, ethanol injection with or without aspiration may be used depending on the operator's preference.