**3. Indications**

292 Aneurysm

mass herniation.

thrombosis and decreases the risk of recanalization.

the case series became progressively larger.

United States of America (USA).

FDA in the US in 2007.

thromboses.

relatively predictable cage that would keep the subsequent coils inside. As one may imagine, the above properties are relatively antagonistic. A coil that penetrates irregular spaces and has a good position to the aneurysm wall is also a coil that may herniate through a large aneurysm neck. In this context of technical difficulty, balloon and stent-assisted techniques have been used to provide protection for the parent artery as well as to treat coil

Intracranial stents also serve as scaffolding for neo-endothelization, providing additional reduction of the flow into the aneurysm. Consequently, their use improves intrasaccular

Even if these concepts seem attractive, manufacturers were rapidly confronted with technical difficulties, such as the narrowness and fragility of the intracranial vasculature, the need to navigate tortuous vessels, and the obligation to provide materials that were thin

The first case of intracranial stenting for treating a brain aneurysm was reported by Higashida et al. in 1997 (Higashida et al., 2005). In that occasion, the authors used a balloonexpandable cardiac stent in combination with Guglielmi detachable coils to treat a fusiform aneurysm of the vertebrobasilar junction. At that time, other authors had already attempted the placement of stent and coils in a fusiform aneurysm in an experimental context in pigs. Soon after, different groups reported a number of strategies using a combination of balloonmounted stents and coils. In 2000, the use of stents for managing coil migration during the treatment of wide neck aneurysms was reported (Fessler et al., 2000, Lavine et al., 2000) and

The first stent specifically designed for the intracranial area to obtain Food and Drug Administration (FDA) approval was the NeuroformTM (Boston Scientific Corporation, Natick, USA). The device was approved for 'humanitarian device exemption' in 2002. This means that its use was complicit to the additional approval of an Institutional Review Board and was supposed to be limited to use on no more than 4000 individuals per year in the

Outside the USA, especially in Europe and in the context of clinical research, other stents became rapidly available. That was the case with the LeoTM (Balt, Montmorency, France), the first self-expanding closed cell design stent released in Europe in 2003, and then the EnterpriseTM (Cordis Neurovascular I., Miami Lakes, USA), which was approved by the

Flow diverters are the last technical advances bringing the concept of 'reverse remodeling' for intracranial aneurysm treatment. SilkTM (Balt, Montmorency, France) and PipelineTM (Chestnut Medical Technologies Incorporation, Menlo Park, CA, USA) are in this category. These devices are intended to exclude the aneurysm sac from the parent artery by creating significant flow disruption, so that blood significantly stagnates inside the aneurysm sac and

enough so that a microcatheter could be placed simultaneously in the vasculature.

For treatment of intracranial aneurysms, stents are used mainly in two different situations: wide neck aneurysm and unfavourable anatomy. Wide neck aneurysm has been defined as a saccular aneurysm in the diameter of the neck larger than 4 mm, in which the dome–toneck ratio is less than 2, or in which the ASPECT ration is superior to 1.6. These circumstances are associated with an increased risk of coil migration and compromising of parent artery patency during non-assisted endovascular coiling. Both situations are not uncommon with large and giant sacciform aneurysms. Circumstances for unfavourable anatomy are MCA trifurcation, neck-to-parent artery diameter <1 and fusiform aneurysms.

The indication stent-assisted endovascular treatment of cerebral aneurysms goes beyond vascular morphology. In the last few years, issues regarding patient selection have received progressively more attention, with the aim of reducing perioperative complications. A candidate for such a procedure must understand the risks and benefits, and be capable of following medical recommendations, especially the use of double antiplatelet therapy. As a consequence, any social and psychiatric conditions in which the compliance of the use of such medications and follow-up are significantly compromised should be considered as relative contra-indications.

Caution should be taken with individuals who may need surgery or a ventricular drainage shortly after the aneurysm treatment - situations that are more frequent with ruptured aneurysms. As the use of antiplatelet medication is mandatory, significant controversy exists on the placement of intracranial stents in the acute phase of intracranial haemorrhage. If subtotal embolization of the aneurysm sac may be performed with coils only, a valuable strategy is to complete treatment in a different session. In such a case, stenting would be performed far from the subarachnoid haemorrhage. Other relative contra-indications are exaggerated; vessel tortuosity, significant atherosclerotic disease and coagulation disorders.
