Long-term angiographic and histopathologic findings in experimental aneurysms of the carotid bifurcation embolized with platinum and tungsten coils.

PURPOSE: To evaluate the long-term outcome of endovascular occlusion of arterial aneurysms effected with metal coils.
METHODS: Microsurgical methods were used to produce carotid bifurcation aneurysms in 20 rabbits and the radiologic and histologic changes were examined. Eight of these aneurysms were occluded with electrically detachable platinum coils (Guglielmi detachable coils [GDCs] and nine were treated with mechanically detachable tungsten coils (mechanical detachable system [MDS]). Three aneurysms remained untreated and served as controls. One animal died of embolic complications 12 hours after endovascular treatment. After observation periods of 3 to 6 months, the remaining animals were examined by intraarterial digital subtraction angiography and subsequent fixation and light and electron microscopy.
RESULTS: Large open spaces without signs of thrombosis were found between the loops of the coil baskets in 12 aneurysms (six treated with GDCs and six treated with MDS) regardless of the observation period. In very densely packed aneurysms (four cases with complete occlusion as determined by angiographic criteria), the coil surfaces were for the most part covered by thin cell layers; however, complete endothelialization was never seen. In aneurysms with an initial partial occlusion of 70% to 90%, coil compaction and/or recanalization was a consistent finding. A comparison of the radiologic findings with the histologic aspect revealed that the degree of occlusion was often overrated on the radiographs (in eight of 17 cases). In general, the fibrous tissue reaction appeared to be slightly more pronounced in aneurysms occluded with tungsten coils.
CONCLUSIONS: Platinum and tungsten coils were not always effective in causing endoluminal thrombosis leading to long-term occlusion by organized thrombus.