with the recurrence rate increasing with time. These results are similar to those previously reported by other endovascular groups. Other studies have questioned whether new matrix coils work better than bare platinum coils. The International Subarachnoid Aneurysm Trial tested the efficacy of endovascular coiling against the traditional micro-surgical clipping. The study initially found very favorable results for coiling, however its results and methodology were criticized. Since the study's release in 2002, and again in 2005, some studies have found higher recurrence rates with coiling, while others have concluded that there is no clear consensus between which procedure is preferred. Risks Risks of endovascular coiling include stroke, aneurysm rupture during the procedure and aneurysm recurrence and rupture after the procedure. Additionally in some patients coiling may not be successful. In general, coiling is only performed when the risk of aneurysm rupture is higher than the risks of the procedure itself. Similar to patients who experience neurosurgical procedures, coiling results in an increase in resting energy expenditure, albeit at a slightly reduced rate than their neurosurgery counterpart. This can lead to malnutrition if steps are not taken to compensate for the increased metabolic rate. Mechanism The treatment works by promoting blood clotting (thrombosis) in the aneurysm, eventually sealing it from the blood flow. This is accomplished by decreasing the amount of blood flow going into the aneurysm, increasing the residence time of the blood (thereby lowering the velocity) in the aneurysm space and reducing the wall shear stress of the aneurysm wall. This change in the blood flow, or hemodynamics, is ultimately dependent on several factors, including: aneurysm type (directly on the parent artery or on a bifurcation of an artery) aneurysm position (relative angle of aneurysm to approaching blood flow) coil packing density angle of parent vessel curvature size of aneurysm neck While these factors are crucial to the success of the procedure, thrombosis ultimately is dependent on biological processes, with the coiling only providing the appropriate conditions for the process to occur, and hopefully closing the aneurysm. Procedure Endovascular coiling is usually performed by an interventional neuroradiologist or neurosurgeon with the patient under general anaesthesia. The whole procedure is performed under fluoroscopic imaging guidance. A guiding catheter is inserted through the femoral artery and advanced to a site close to the aneurysm after which angiography is performed to localize and assess the aneurysm. After this, a microcatheter is navigated into