Current concepts of endovascular aneurysm treatment, and about the role of stents for endovascular repair of cerebral arteries

Abstract

Within the last 15 years, image-guided minimally invasive endovascular treatment for ruptured or un-ruptured cerebral aneurysms has surpassed surgical treatment for a subset of aneurysms, as shown in recent large randomised trials (ISAT, ISUIA). Endovascular patient care occurs at equal or lower cost than surgery. Cerebral aneurysms are of variable pathogenesis and by far the largest group consists of saccular aneurysms formed at proximal cerebral vessel bifurcations. Likely based on a focal vessel wall weakness, fragile out-pouchings typically develop in areas of high shear stress and at areas of the vessel tree where there is higher intravascular pressure, i.e. along the proximal intracranial branching of the internal carotid artery and less frequently of the vertebro-basilar system. Initiation, growth and rupture of an aneurysm are likely driven by a combination of several factors, each contributing to a variable degree in each of the evolutionary steps of an aneurysm's history. Current treatment modalities include for open surgical treatment various techniques to reconstruct the artery (clips) or to reinforce the aneurysm wall (wrapping) or to bypass circulation of the vessel carrying an aneurysm (aneurysm trapping and bypass surgery). Less invasive, endovascular treatment techniques have been based on the principles of aneurysm filling with coils or polymers or vessel occlusion (aneurysm trapping). More recently, vessel reconstruction with stents rather than aneurysm filling has been advocated as treatment (Lylyk et al., J Neurosurg 2002;97: 1306-13). Both coils and stent techniques aim to induce slowing of blood flow and initiation of thrombosis within the aneurysm. Secondary vessel wall repair with scar tissue occurs within weeks. With small vessel wall defects (focal defects, usually less than 3-4 mm in maximum diameter), coil implantation seems to allow successful repair under this principle, provided that the lumen of the aneurysm pouch is suitable for coil introduction. With larger vessel wall defects in proportion to the vessel diameter (segmental defects), either the vessel must be occluded if tolerated by the patient, or the vessel is reconstructed with the use of stent implants. Based on initial clinical experience, stents seem to offer advantages over coils alone in the endovascular repair of segmental arterial wall defects. However, more research is required to better understand this stent function and to adapt stent technology to the new role it is asked to play in the intracranial circulation: repairing vessels with an aneurysm rather than opening a stenosis as typically requested in coronary or peripheral vessels. The following text is an update on current concepts and treatment, and how medical informatics is about to influence patient management by better lesion understanding, treatment simulation, implant design and medical engineering.