Endovascular techniques (through the blood vessel) may be used to completely close an arteriovenous malformation or they may be deployed to complement another treatment such as microsurgery or stereotactic radiosurgery by either reducing the flow through the AVM or decreasing the nidal volume in hopes of rendering treatment safer and/or more likely to be curative.
Typically embolisation is carried out under a general anaesthetic which assures the patient remains completely still while the catheter is manoeuvred into deeper parts of the circulation and also affords tight control over the blood pressure and use rate to assure optimal conditions for the procedure. Tiny catheters are passed into the circulation
under< x-ray guidance they are directed through the blood vessels of the brain to the malformation. Most often the arteries are used to deliver the embolic material (trans-arterial) although there are circumstances when material is delivered through veins (transvenous) or a combination of both.
Embolisation can curative in AVMs with particularly favourable architectures. As the architecture increases in complexity and the nidus in size the likelihood of obliterating the arteriovenous shunt reduces and/or the risks of doing so increase. In our current practice embolisation is relied on more to complement microsurgical or radiosurgical treatment rather than to push for cure. Procedural risks are not better compared to other therapies and the occlusion rates are lower in the long term. On the other hand dural and pial arteriovenous fistulae lend themselves very well to endovascular treatment in most cases. As with procedure case selection is key to success.
N-butyl cyanoacrylate (NCBA) glue is a relative of the original superglues applied to vascular disease. A related glue was first used in 1975. Because it adhered to the vessels, catheter and set very rapidly controlling its deployment could be challenging as this can lead to problems such as blockage of catheters, adhesion to the tissues or loss of access to the AVM through premature proximal occlusion as well as inadvertent blockage of non-AVM vessels. Diluting the glue with other chemicals made for a more pliable substance. Ultimately the glue induces an inflammatory reaction in the tissues with fibrosis of blood vessels in the long term.
More recently liquid embolic agents which do not adhere to the inner surface of the vessels have been developed. The first of these in use was Onyx , the trade name for ethylene vinyl alcohol copolymer. It is combined with tantalum powder to make it visible on x-ray and offers additional control and predictability as it solidifies compared to NBCA. For examples injections can stop and start again in a way not oossible with a rapidly setting material. Again it is available in a variety of concentrations. The catheters through which it is administered are first flushed with a chemical called dimethylsufoxide (DMSO). The patient and those around them may be aware of a characteristic odour that lingers for 24 hours or so after treatment, the result of DMSO being expelled throught the skin and mucus membranes.
SQUID is a newer EVOH agent with purportedly longer injection times and it is appears dense on x-ray allowing easier visualisation of vessels later in the procedure. PHIL (Precipitating Hydrophobic Injectable Liquid) is another with the benefit of prepreparation and less wastage. There are no high quality comparative studies between these agents to suggest any one is superior. Your treating interventional Neuroradiologist will be happy to discuss these agents further with you.
Aneurysms on arteries irrigating an AVM may be coiled as with aneurysms in other locations. If the the rest of the AVM remains in-the coils may be subject to excessive compaction and a higher likelihood of aneurysm recurrence than with non-AVM aneurysms. Coils may also be used to occlude larger vessels and selected nidal elements.
Poly Vinyl Alcohol (PVA) particles can there to vessel walls as well as occluding vessels by aggregating and mechanically obstructing them. They have been largely supplanted by liquid embolic in brain AVM but may still be deployed in selected cases or tumour embolisations. Gelatin spheres provide another mechanical alternative. Many other temporary occlusive materials have been used in the past including Gel Foam, silk or Vicryl suture materials.