Onyx (Medtronic, Minneapolis, MN, USA) is a non-adhesive liquid embolic agent composed of an ethylene vinyl alcohol (EVOH) copolymer dissolved in dimethyl sulfoxide (DMSO). Onyx is explicitly designed for use in interventional neuroradiological procedures. Onyx’s unique formulation allows controlled delivery and solidification within the target vessel, providing durable occlusion of abnormal vascular structures such as arteriovenous malformations and dural arteriovenous fistulas. This report reviews the basic understanding of the use of Onyx in interventional neuroradiology. The hydrophilic properties of the agent facilitate its smooth delivery through microcatheters, ensuring precise navigation and deposition within vascular malformations under fluoroscopic guidance. When Onyx was injected into the target vessel, the vessel was embolized as the solvent (DMSO) diffused into the blood and EVOH precipitated to form a durable cast. Onyx liquid embolic agents substantially advance the endovascular treatment of intracranial vascular lesions.

Various types of embolic substances are used in endovascular therapy, and understanding their characteristics, including shape and kinetics, is essential for proper use. Cyanoacrylate is a typical liquid embolization agent that can be applied to many cerebral neurovascular lesions. It is injected as a mixture with ethiodized oil to provide radiopacity and regulate the polymerization rate. This review describes the characteristics, action mechanisms, techniques of use, and potential pitfalls of using cyanoacrylate-ethiodized oil mixtures for embolization.

This review discusses the use of N-butyl cyanoacrylate (NBCA) in various neuroendovascular treatments. Despite the increase in the ONYX, NBCA continues to have significant usage. It is particularly useful for the treatment of arteriovenous malformations (AVM) and dural arteriovenous fistulas (dAVFs). Comparative studies have suggested that ONYX and NBCA are equally effective and safe for the treatment of AVM. However, the choice between the two depends on specific situations, such as the characteristics of the feeding arteries. NBCA is recommended for tortuous feeders, high-flow fistulous feeders, and feeders with a short margin of reflux, owing to the procedural risks posed by ONYX. The use of NBCA is also prominent in dAVF embolization. While achieving total occlusion solely with NBCA can be challenging, NBCA adheres to the vessel wall and encourages thrombus formation, aiding in fistula obliteration. In addition to AVM and dAVF, NBCA is used to treat chronic subdural hematoma and craniofacial vascular injuries. Embolization using NBCA is beneficial because of its deep penetration into the target tissue. For craniofacial injuries, NBCA embolization provides secure hemostasis within a short time. Neuroendovascular physicians should understand the characteristics of NBCA as a liquid embolic material and have expertise in the technical aspects of NBCA embolization, even in the ONYX era.