Zur endovaskulären Therapie intrakranieller Aneurysmen mit verschiedenen Stents : eine experimentelle Analyse im Tiermodell

摘要

The rupture of cerebral aneurysms causing subarachnoid hemorrhage (SAH) is associated with high morbidity and mortality. Recurrent hemorrhage after acute SAH by re-rupture occures in more than 20% and poses a serious threat to the patient with often devastating consequences. Therefore, treatment of ruptured aneurysms is mandatory. While Guglielmi detachable coil (GDC) systems have been widely accepted as an endovascular treatment option, primary stenting of aneurysms using porous stents, stentgrafts, or implantation of coils after stent placement constitute emerging but still experimental techniques in endovascular treatment strategies. The aim of the present study was to use an animal model to investigate these different approaches to treat cerebral aneurysms concerning the rate of closure, the histopathological changes within the aneurysm cavity and the parent vessel after stent placement. We created aneurysms in 30 rabbits by distal ligation and intraluminal incubation of the right common carotid artery with elastase. This enzyme digested the internal elastic lamina leading in subsequent aneurysmatic dilatation of the thus created vessel stump. 10 animals were treated with porous stents alone and 10 rabbits with stentgrafts (polyurethane covered stents). Furthermore 10 animals were treated with the current gold standard by using electrolytically detachable coils. Five animals in each group were observed for 1 month, the other animals were observed for 3 months. After the observation period a DSA series was performed to evaluate the final angiographic results. Thereafter, the animals were euthanasized and the brachiocephalic trunk, the right subclavian artery up to the vertebral artery and the aneurysm were resected en bloc and rapidly fixed in paraformaldehyde solution. Each group was subdivided and underwent macroscopical investigation, microscopical investigation after unhinging stents and coils, and microscopical investigation including the endovascular devices. Histological analyses included immunohistochemical investigations for estimating the proliferation of the intima and possible inflammatory infiltration. Covered stents led to a complete and stable aneurysm occlusion with only minimal proliferative carrier vessel wall changes. Onlly mild in-stent stenosis was found in three animals after three months. The aneurysms were completely occluded with partly organized thrombotic material. Fibrotic changes were seen between the aneurysm wall and thrombus. Porous stents initially led to intraaneurysmatic blood flow alterations in 9 of 10 cases. But after one month only one aneurysm seemed occluded in angiography wereas 2 aneurysms showed complete occlusion in the three-month follow-up group. In one case progressive sprouting of neointima inside the carrier vessel was present, which resulted in a stenosis of up to 90%. Intraaneurysmatic thrombus organization was poor or even absent respectively. In the “Coil” group only 2 aneurysms demonstrated complete occlusion in angiography after one month. After three month all aneurysms were again perfused following coil compaction with visualisation of a neck remnant. The study demonstrates the possible shortcomings and problems of emerging “Stent-techniques” to treat intracerebral aneurysms and concludes the following aspects:1. Porous stents placed over the orifice of an aneurysm can alter blood flow paterns leading to reduced blood inflow or blood stasis within the aneurysm. Therefor induction and promotion of thrombus formation within the aneurysmal lumen is possible.2. However this method remains highly reliant on chance, since it seems unpredictable whether or not an aneurysm will be occluded on follow-up. Moreover, it has to be determined whether the occlusion of the aneurysm remains stable over time leading in a reduced risk of re-rupture.3. Covered stents led to complete and stable aneurysm occlusion and induced progressive thrombotic organization within the aneurysm.4. The prober delivery of the stent at the orifice of an aneurysm stays difficult, concerning parent vessel curvature, the navigation through intracanial arteries and the potential occlusion of small perforating arteries. 5. A tendency towards progressive vessel wall reaction should be considered for each stent. Though polyurethane coated stents seem to cause increased neointimal proliferation, possibly due to chronic inflammatory reactions. Therefor we presume that further advances in stent materials and coating might help to overcome this problems.