The most commonly used embolic agent in brain AVMs is the fast polymerizing liquid adhesive n-butylcyanoacrylate (NBCA, Histoacryl; Braun, Melsungen, Germany). Pure NBCA polymerizes immediately after contact with blood. Slower polymerization is achieved when NBCA is mixed with iodinated oil (Lipiodol; Guerbet, Roissy, France). The use of a high concentration of NBCA or pure NBCA in high-flow shunts in brain AVMs may occlude the fistula within seconds, but this technique requires courage, experience and skill, since flow of NBCA is to some extent unpredictable . Inadvertent migration of the glue into the draining veins may result in immediate haemorrhage by blocking venous outflow. Detachable coils may be inserted at the fistula site to decrease the flow and thereby facilitate the injection of NBCA . Recently, the new liquid embolic agent Onyx has become available for embolization of brain AVMs (Onyx Liquid Embolic System; Microtherapeutics, Irvine, Calif.). Onyx is nonadhesive and polymerizes slowly. Onyx is available in several concentrations and the high-concentrated Onyx can be used to slowly occlude large AV shunts or pial AV fistulas in a more controlled way than that achieved with NBCA . However, simple Onyx injection is not always feasible: in some very high-flow shunts Onyx may migrate through the fistula into the distal draining veins. We found the adjuvant use of a microballoon to block the flow to enable gradual occlusion of the large high-flow shunts with Onyx in the AVM of patient 1 a very useful approach.
In the other patients, one with a very short arterial feeder of an AV shunt in an AVM and one with a side-wall pial fistula, the use of liquid embolic agents was not possible and controlled delivery of detachable coils to the venous side of the shunt was technically easy with complete occlusion of the fistula. This technique is helpful in shunts with a moderately dilated venous outflow tract in which placement of coils is possible.
In conclusion, different types of high-flow AV shunts can safely be occluded with endovascular techniques tailored to the specific anatomical configuration of the shunt.