Endovascular Treatment of Intracranial Aneurysms

Abstract

The endovascular treatment of intracranial aneurysms has evolved over the last decade from a timid alternative to surgical clipping to a very well accepted universally expanding form of therapy. Recent randomized clinical trials (ISAT) have legitimized the advantages of the endovascular treatment over surgery. The mainstay of the endovascular treatment is the electrically detached platinum coil introduced in the early nineties by Guido Guglielmi (GDC). The GDC influenced favorably the acceptance of endovascular treatment of aneurysms due primarily to its efficacy, ease of use and reliability. More and more physicians from different disciplines have learned the basic techniques of endovascular treatment and are now practicing them. The associated mortality and morbidity continue to improve steadily. Several improvements have been made to the GDC which have resulted in a better safety record and better long term anatomical results. These improvements include: a smaller gauge primary wire, a “soft” and “ultrasoft” version, a faster and more reliable detachment mechanism, a stretch-resistant coil, etc. However, and despite these improvements, there remains a major drawback to the use of GDC which is the poor long term anatomical results, i.e. high recanalization rate, in large and giant aneurysms and in aneurysms with a wide neck. Whereas the long term anatomical results are good in small aneurysms with small neck, large aneurysms with wide neck have an unacceptably high rate of recanalization of at least 20 to 30%. Several new technologies have emerged for the purpose of improving the efficacy of bare platinum coils. These include: 1 - New complex-shaped coils that conform better to complex-shaped or large aneurysms and therefore produce a better obliteration rate, particularly in the long term. 2 - Faster detachment mechanism which is more reliable than the original electrolytic detachment. 3 - Adding an expansile material to the platinum coil such as hydrogel to improve the fill-factor of the aneurysm and therefore the long term obliteration rate. 4 - Modifying the surface of the platinum coils to induce more fibrous tissue within the aneurysm and therefore accelerate the healing process. The surface modifiers that have been used so far include a polyglycolic acid (PGLA) polymer and a radioactive isotope (P32). In addition to modifying platinum coils, other devices have been introduced as adjuncts to coiling. These include: 1 - The Trispan® neck bridge device designed primarily to aid in the packing of terminal and bifurcation wide-neck aneurysms with platinum coils. 2 - Low-profile balloon-expandable metallic stents designed primarily for the reconstruction of the parent artery in large and wide-neck aneurysms. 3 - Flexible and low-profile self expanding stents made of Nintinol and designed for the reconstruction of the parent artery. 4 - Flexible covered stents designed to exclude large and giant aneurysms from the Parent Circulation. Other embolic agents have also been developed either as replacement or adjunct to platinum coils in the endovascular treatment of aneurysms. These include: 1 - Ethyl Vinyl Alcohol (EVOH) polymer dissolved in Dimethyl Sulfoxide (DMSO) commercialized under the trade name of Onyx®. 2 - Derivatives of Cyanoacrylate such as Neuracryl®.