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Preventing rebleeding

In general, the decision between clipping and coiling is made on the basis of the location of the aneurysm, its size and the condition of the person. Aneurysms of the middle cerebral artery and its related vessels are hard to reach with angiography and tend to be amenable to clipping. Those of the basilar artery and posterior cerebral artery are hard to reach surgically and are more accessible for endovascular management. These approaches are based on general experience, and the only randomized controlled trial directly comparing the different modalities was performed in relatively well people with small (less than 10 mm) aneurysms of the anterior cerebral artery and anterior communicating artery (together the "anterior circulation"), who constitute about 20 percent of all people with aneurysmal SAH. This trial, the International Subarachnoid Aneurysm Trial (ISAT), showed that in this group the likelihood of death or being dependent on others for activities of daily living was reduced (7.4 percent absolute risk reduction, 23.5 percent relative risk reduction) if endovascular coiling was used as opposed to surgery. The main drawback of coiling is the possibility that the aneurysm will recur; this risk is extremely small in the surgical approach. In ISAT, 8.3 percent needed further treatment in the longer term. Hence, people who have undergone coiling are typically followed up for many years afterwards with angiography or other measures to ensure recurrence of aneurysms is identified early. Other trials have also found a higher rate of recurrence necessitating further treatments.