Electrolytically Detachable Microcoils

Dr Sadato and colleagues have shown the utility of electrothrombosis in the treatment of a complex dural fistula (1). They are to be congratulated on their fine work. The treatment of dural fistula from the transvenous approach is often the only way to exclude the lesion completely. In their case, it was quite difficult to eradicate the fistula by using standard coils. Their postulate that the electrothrombosis induced by their experimental detachable coils was a primary factor in finally curing the fistula is reasonable. We have used the Guglielmi detachable coil (GDC) for high-flow fistulae. In March 1990, after more than 1 year of laboratory work and several stages of technical refinements, the GDC microcoils became available for clinical use under a strict FDA-approved protocol (2 , 3). Since then, we have had the opportunity to treat nine patients with fistulous lesions utilizing the GDC system: five patients had spontaneous dural-type carotidcavernous fistulae treated by transvenous approach, three patients had high-flow carotid-cavernous fistulae (two traumatic and one due to a ruptured intracavernous aneurysm), and one patient had a posttraumatic vertebra-vertebral fistula. This technique has proved to be useful in cases in which it was necessary to cast the cavernous sinus, because these particular microcoils are very pliable and adapt to the morphology of the cavernous sinus without producing significant mass effect to the intracavernous cranial nerves (4). The detachable microcoils are also useful because one is able to predict their behavior before detachment, important information in high-flow fistulae with recruitment of large cerebral cortical veins. The retrieveability of the coils allows for more flexibility in the choice of coil size, without the risk of inadvertent migration . Furthermore, the pliability of these coils can be an advantage in areas where access is difficult. A problem that can occur with standard coils is the "kickback" of the microcatheter while depositing the coil , especially when the coil is larger than the diameter of the vascular lumen. With the GDC, this is not a great problem, and a tighter packing can be obtained. Finally, we agree with Sadato et al that electrothrombosis plays a significant role in the development of clot/occlusion of the fistula . However, we have found that electrothrombosis alone is insufficient to insure occlusion of either a fistula or an aneurysm, and that tight packing is essential. On reviewing Dr Sadato 's article , one notices that their coil appears to be similar to the GDC system, with two distinct differences. First, the material between the delivery wire and the platinum coil is copper. Copper can be toxic in high doses and this could be a consideration when embolizing with multiple coils. Second, the platinum coil itself appears to closely resemble the standard commercial microcoils, which are significantly stiffer than the GDC. We do not have information about the technical characteristics of their detachable microcoil (length and diameter of platinum coil and delivery wire , insulation of the delivery wire, physical characteristics of delivery microcatheter). Also , their guiding catheter system does not appear to have safety markers in the coil and in the microcatheter to indicate when the junction between the platinum coil and the stainless steel is beyond the tip of the microcatheter (Fig. 1). We have found that this technical refinement is indispensable for the embolization of small or acute aneurysms, because of the possibility of aneurysm perforation by the stiffer stainless steel portion of the detachable microcoil. Also , in cases in which multiple coils have been placed , it can be difficult to actually determine when the coil has left the catheter (Fig. 2).