In Re: Radiologic and Histopathologic Evaluation of Canine Artery Occlusion After Collagen-Coated Platinum Microcoil Delivery

I read with interest, in the April 1999 issue of AJNR, the article of Tamatani and colleagues (1) on the evaluation of endovascular collagen-coated coils in the experimental setting, and the relative editorial of Berenstein on future developments of coils for aneurysms (2). In our field of endovascular neurosurgery, we all have seen in recent years many experimental articles dealing with surface modifications of coils, collagen added to coils, coatings added to coils, etc. The appropriate references are all in the thorough and articulate article of Tamatani and colleagues (1).

I would like to comment on the sentence of Dr. Berenstein: “The delivery of coated or biologically altered coils into the aneurysmal lumen seems to be a promising method for producing intravascular scars, and may represent a revolution in the management of presently unmanageable lesions.” I sincerely hope that Dr. Berenstein is right. We have to consider, however, that regular GDCs, because of their malleability and elasticity, may partially absorb the pulsatile energy of the blood circulation by damping the acute spike of the systole and gradually redistributing the systolic energy to the entire wall of the aneurysm. In other words, coils may act as the shoreline that transforms the waves of the sea into a continuous motion of the water. I cannot imagine any other explanation for why, as Dr. Berenstein suggests, even subtotally coiled aneurysms have a low (re)bleeding rate. If this is true, then the fact that GDCs do not induce a “scar” would be a “good thing.” I do not know if an intra-aneurysmal scar would improve aneurysm healing or would act as a hammer toward any residual portion of the aneurysm. A scar could induce retraction of the walls of the parent vessel with consequent stenosis. Unlike coiling or clipping, a scar could offer a wide, stiff surface to the systole with unknown effects on the parent artery and on any residuum of the aneurysm. One thing is certain—with an intra-aneurysmal scar, we would lose forever the shock-absorbing effect of the coils. In any event, experimental aneurysms are so different from their human counterpart that any extrapolation of medium long-term results would be inaccurate. As often happens in science, there was some casualty and luck in 1989–1990 when our experimental work (that led to the GDCs) was also successful in patients. I do not intend to dampen the enthusiasm of clinicians who aim to change GDCs with bioactive materials in order to obtain a more stable aneurysm occlusion. Nevertheless we will have to be very cautious in expanding experimental findings beyond their boundaries.