Porous Stent Research Articles

Endovascular Treatment of Small Intracranial Aneurysms: Three Alternatives to Coil Occlusion

Small intracranial aneurysms with a fundus diameter of 2 - 3 mm may rupture and are therefore potential targets for an endovascular approach in treatment. Currently available coil technology is less than optimal for the treatment of aneurysms within this size range. Even the smallest coils are sometimes too large. If such a minute coil can be introduced into a small aneurysm, the hemodynamic effect and the induced thrombosis are frequently inadequate to occlude the aneurysm sufficiently from the parent artery circulation. Three technical alternatives for the endovascular treatment of small intracranial aneurysms not suitable for coil occlusion are illustrated with the following three case descriptions. Stent grafts are usable for the intracranial internal carotid artery and for the V4 segment. The stiffness of the stent and the high expansion pressures are the two major drawbacks. Coaxial deployment of two or more self-expanding porous stents can result in sufficient redirection of the blood flow to induce aneurysmal thrombosis. Deployment of multiple stents, however, may require several treatment sessions in order to allow for the integration of the stents into the vessel wall from session to session. A regular microcatheter can block aneurysmal inflow in aneurysms with a very narrow neck. This allows the occlusion of the aneurysm with an appropriate amount of highly concentrated, rapidly polymerizing glue. Polymer emboli may result from excessive or rapid glue injection. The available coil technology has inherent limitations in the treatment of very small intracranial aneurysms. Liquid embolic agents and stent-based extrasaccular treatment strategies may provide solutions for these challenging lesions.

Pathology of Stented Common Carotid Aneurysm in Dogs

To elucidate focal successive histological responses of the neck of wide-necked aneurysm after single stent implantation and stent-assisted coiling, an experimental wide-necked aneurysm model was surgically created in bilateral common carotid arteries of adult dogs. Balloon-expandable porous stents were positioned across the aneurysm necks on both sides. The aneurysm cavity of one side was additionally loosely coiled with Gugliemi detachable coils after stent implantation. The dogs were followed up with ultrasonography and angiography, then sacrificed at two days, one month, and one year and the aneurysm specimen was subjected to macro, micro, and electron microscopic observation. Stent implantation and coiling was successful in eight dogs. This investigation observed that single stent implantation slowed down the blood flow within the aneurysm, but barely induced thrombosis within the aneurysm. There was neointima formation over the stent mesh without thrombus within the aneurysm cavity, but it did not cover the whole aneurysm neck at one year.Aneurysms treated with stent-assisted coiling showed thrombosis within the aneurysms and neointima formation over the whole aneurysm orifice. These results suggest that the neointima could develop over bare stent filament without thrombus within the aneurysm cavity, coils could enhance thrombosis within the aneurysm cavity and facilitate neointima formation over the aneurysm orifice. Stent-assisted coiling may be an alternative option for the treatment of wide-necked aneurysms.

Treatment of Experimentally Induced Aneurysms with Stents

Although Guglielmi detachable coil systems have been widely accepted for treatment of intracranial aneurysms, primary stenting of aneurysms using porous stents, stent grafts, or implantation of coils after stent placement constitute emerging techniques in endovascular treatment. The aim of the present study was to use an animal model to investigate these different approaches to treat cerebral aneurysms with regard to the rate of closure and 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. Ten animals were treated with porous stents alone, 10 animals with stent grafts (covered stents), and 10 animals with stents and additional coiling via the interstices of the stent, which enabled dense packing of the coils. Five animals in each group were observed for 1 month and the other animals for 3 months. Histological analyses were performed, including 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. One covered stent was completely occluded with old thrombus, and the other 9 remained patent. Porous stents occluded two of five aneurysms in the 1-month follow-up group and four of five after 3 months. However, progressive sprouting of neointima inside the carrier vessel that resulted in a stenosis of up to 40% was present. In the Stent + Coil group, one aneurysm showed recanalization after 1 month, and three of five aneurysms were recanalized after 3 months after coil compaction. Moreover, in-stent stenosis of up to 30% was present. This study demonstrates the possible shortcomings and problems of emerging stent techniques to treat intracerebral aneurysms, shows where technical advances have to be made, and describes in which cases of aneurysm morphology caution has to be exercised when considering an endovascular approach using stents.

Free Recovery Effects of Shape-Memory Polymers for Cardiovascular Stents

AbstractThe shape-memory effect was examined in polymer stents intended for cardiovascular applications. Four polymer networks were synthesized from poly(ethylene glycol) dimethacrylate and tert-butyl acrylate with 10 wt% and 20 wt% crosslinker, and with glass transition temperatures (Tg) of 52°C and 55°C. Solid and 50% porous stents were manufactured and tested for free strain recoverability at temperatures at or just above 37°C. Stents with lower glass transition temperatures and a higher degree of crosslinking recovered faster than their counterparts. Lower deformation (packaging) temperatures and higher recovery temperatures induce more rapid recovery. The presence of geometrical features, such as pores, initiated recovery sooner, but had negligible influence on overall recovery.

A lattice Boltzmann study of blood flow in stented aneurism

The treatment of cerebral aneurisms with a porous stent has recently been proposed as a minimally invasive way to prevent rupture and favor coagulation mechanism inside the aneurism. The efficiency of a stent is related to several parameters which are not yet fully understood. The goal of this paper is to identify, through numerical simulations, how the stent structure and its positioning affect the hemodynamics properties of the flow inside the aneurism. We use the concept of flow reduction to characterize the stent efficiency. Our simulations are based on a lattice Boltzmann modeling of blood flow. Our results, which agree well with in vitro experiments, show how the various parameters play a role and help us to understand the phenomena.

Treatment of traumatic aneurysms and arteriovenous fistulas of the skull base by using endovascular stents.

The authors describe their preliminary clinical experience with the use of endovascular stents in the treatment of traumatic vascular lesions of the skull base region. Because adequate distal exposure and direct surgical repair of these lesions are not often possible, conventional treatment has been deliberate arterial occlusion. The purpose of this report is to demonstrate the safety and efficacy as well as limitations of endovascular stent placement in the management of craniocervical arterial injuries. Six patients with vascular injuries were treated using endovascular stents. There were two arteriovenous fistulas and two pseudoaneurysms of the distal extracranial internal carotid or vertebral arteries resulting from penetrating trauma, and two petrous carotid pseudoaneurysms associated with basal skull fractures. In one patient a porous stent placement procedure was undertaken as well as coil occlusion of an aneurysm, whereas in the remaining five patients covered stent grafts were used as definitive treatment. There were no procedural complications. One patient in whom there was extensive traumatic arterial dissection was found to have asymptomatic stent thrombosis when angiography was repeated 1 week postoperatively. This was the only patient whose associated injuries precluded routine antithrombotic or antiplatelet therapy. Follow-up examinations in the remaining five patients included standard angiography (four patients) or computerized tomography angiography (one patient), which were performed 3 to 6 months postoperatively, and clinical assessments ranging from 3 months to 1 year in duration (mean 9 months). In all five cases the vascular injury was successfully treated and the parent artery remained widely patent. No patient experienced aneurysm recurrence or hemorrhage, and there were no thromboembolic complications. The authors' experience demonstrates that endovascular treatment of traumatic vascular lesions of the skull base region is both feasible and safe. The advantages of minimally invasive stent placement and parent artery preservation make this procedure for repair of neurovascular injuries a potentially important addition to existing methods.

Abstracts of literature

Abstracts of literature

Intravascular stents for intracranial internal carotid and vertebral artery aneurysms: preliminary clinical experience

Results of previous in vitro and in vivo experimental studies have suggested that the placement of a porous stent within the parent artery across the aneurysm neck may hemodynamically uncouple the aneurysm from the parent vessel, leading to thrombosis of the aneurysm. For complex wide-necked aneurysms, a stent may also aid the packing of the aneurysm with Guglielmi detachable coils (GDCs) by acting as a rigid scaffold that prevents coil herniation into the parent vessel. Recently, improved stent system delivery technology has allowed access to the tortuous vascular segments of the intracranial system. The authors report here the intracranial stenting of aneurysms involving different segments of the internal carotid artery (ICA) and the vertebral artery (VA). Four patients with intracranial aneurysms located at the petrous, cavernous, and paraclinoid segments of the ICA and at the VA proximal to the origin of the posterior inferior cerebellar artery, respectively, were treated since January 1998. In three of these patients, stent placement across the aneurysm neck was followed by GDC placement, accomplished via a microcatheter through stent mesh. In one patient, the aneurysm was treated solely by stenting. No periprocedural complications were observed, and at follow up, no patient was found to have suffered symptoms referable to aneurysm growth or thromboembolic complications. More than 90% occlusion of the aneurysm was achieved in the three cases treated by stenting and GDC placement. One of these patients underwent 6-month follow-up angiography that did not reveal any in-stent stenosis. In the case treated solely by stent placement, no evidence of aneurysm thrombosis was observed either immediately postprocedure or on follow-up angiography performed 24 hours later. A new generation of flexible stents can be used to treat intracranial aneurysms in difficult-to-access areas such as the proximal intracranial segments of the ICA or the VA. The stent allows tight coil packing even in the presence of a wide-necked, irregularly shaped aneurysm and may provide an endoluminal matrix for endothelial growth. Although convincing experimental evidence suggests that stent placement across the aneurysm neck may by itself promote intraluminal thrombosis, the role of this phenomenon in clinical practice may be limited at present by the high porosity of currently available stents.

Alteration of hemodynamics in aneurysm models by stenting: influence of stent porosity.

Recent developments in minimally invasive approach to cerebrovascular diseases include the placement of stents in arteries for treatment of aneurysms. Preliminary clinical observations and experimental studies have shown that intravascular stents traversing the orifice may lead to thrombosis and subsequent occlusion of the aneurysm. The alterations in vessel local hemodynamics due to the introduction of a stent are not yet well understood. We investigated changes in local hemodynamics resulting from stent implantation. Pulsatile flow patterns in an experimental flow apparatus were visualized using laser-induced fluorescence of rhodamine dye. The test cells were constructed in a rectangular shape to facilitate an undisturbed longitudinal view of flow patterns in parent vessel and aneurysm models with and without porous stents. Woven nitinol stents of various porosities (76%, 80%, 82%, and 85%) were investigated. The selected fluid dynamic similarity parameters (Reynolds and Womersley numbers) represented conditions usually found in high-flow, larger arteries in humans (such as the carotid artery) and low-flow, smaller arteries (such as the vertebral artery). The mean Reynolds number for the larger arteries was 180, with maximum/minimum values of 490/-30 and the Womersley number was 5.3. The mean Reynolds number for the smaller arteries was 90, with maximum/minimum values of 230/2, and the Womersley number was 2.7. For the larger arteries modeled, placement of a stent of the lowest porosity across the aneurysm orifice resulted in reduction of aneurysmal vortex speed and decreased interaction with parent vessel flow. For smaller arteries, a stent of the same porosity led to a substantial reduction of parent vessel/aneurysmal flow interaction and the appearance of a nonrecirculating crescent of fluid rich in rhodamine dye in the aneurysm dome. Our results can help explain in vivo thrombus formation within an aneurysm after placement of a stent that is compatible with local hemodynamics.

Utilità délla TC a strato sottile, secondo piani coronali diretti, nello studio del massiccio facciale

Lo studio TC della regione del massiccio facciale si è andato affermando e viene richiesto con sempre maggiore frequenza per le dettagliate informazioni anatomiche che riesce a fornire, consentendo un preciso bilancio pre-operatorio in rapporto anche alle nuove tecniche chirurgiche perendoscopiche. Scopo del lavoro è quello di ottimizzare i parametri tecnici dell'esame TC, prendendo in considerazioni aspetti quali il posizionamento del paziente e l'impostazione dell'esame, con particolare riguardo al rapporto fra dettaglio anatomico e dose erogata, e la normale anatomia della regione per strati successivi.