OMPARATIVELY speaking, the morbidity and mortality rates associated with the rupture and treatment of aneurysms located in the anterior circulation carry a better prognosis than those in the posterior circulation. 11 This fact is partly due to the surgical difficulties related to BA bifurcation aneurysms. Unfortunately, aneurysms of the BA bifurcation are the most common in the posterior circ- ulation (~ 50% of posterior circulation aneurysms, but on- ly ~ 5% of all intracranial aneurysms). Microneurosurgical approaches are often challenging given that these lesions are deeply located, confined in a narrow anatomical space (the interpeduncular fossa), surrounded by important perfo- rating arteries, and in close relation to the diencephalon, es- pecially large and giant aneurysms. 10 Endovascular techniques have evolved significantly over the last three decades, with major improvements in angi- ography, microcatheter, and coil technologies, although the underlying principles involved in treating intracranial aneu- rysms through occlusion with metal coils were described long ago. 29 Within the last decade, in particular, endovascu- lar coil occlusion of intracranial aneurysms has evolved from an experimental alternative to a widely accepted meth- od. 28 Radiological and clinical results achieved with the use of detachable coils to obliterate aneurysms, particularly those arising at the BA tip, have been encouraging. 2 Endo- vascular coil occlusion carries relatively low morbidity and mortality rates, significantly reduces the risk of (re)bleed- ing, and allows for the safe implementation of aggressive measures intended to prevent delayed cerebral ischemia due to vasospasm. 15 More recently, analysis of large-scale ran- domized trials and data registries has revealed the clinical effectiveness of coil occlusion for ruptured as well as unrup- tured intracranial aneurysms. 17,28 In the present study we aimed to compare the results of the endovascular procedures performed at a single institu- tion, in terms of both safety and efficacy, with data pub- lished by other neuroendovascular teams. J Neurosurg 103:990–999, 2005 990 Angiographic and clinical results in 316 coil-treated basilar artery bifurcation aneurysms HANS HENKES, M.D., SEBASTIAN FISCHER, M.D., W AGNER MARIUSHI, M.D., WERNER WEBER, M.D., THOMAS LIEBIG, M.D., ELINA MILOSLAVSKI, M.D., STEFAN BREW, M.D., AND DIETMAR KÜHNE, M.D. Klinik für Radiologie und Neuroradiologie, Alfried Krupp Krankenhaus, Essen, Germany Object. The aim of this study was to analyze the effect of the endovascular treatment of basilar artery (BA) bifurcation aneurysms and to compare the results with those published by other neuroendovascular teams. Methods. The authors performed a retrospective analysis of 316 aneurysms of the BA bifurcation that had been treated using endovascular coil occlusion between November 6, 1992, and February 12, 2005. After the initial embolization proce- dure, a 90 to 100% occlusion rate was achieved in 86% of the aneurysms. No complication was evident in 80% of the le- sions, although periprocedural aneurysm rupture (3.2%) and thromboembolic events (12.3%) were the most frequent complications. Clinical outcome according to the Glasgow Outcome Scale (GOS) was a score of 5 or 4 in 77%, 3 in 11%, 2 in 5%, and 1 in 7% of patients. Initial follow-up angiography studies were obtained in 56% of patients at a mean of 19 months posttreatment and demonstrated a 90 to 100% occlusion rate in 70%. No recurrence was seen on 65% of the aneu- rysms. Coil compaction was evident on 24% of the follow-up angiograms. A second treatment was performed on 48 aneurysms (15%) a mean of 27 months after the first therapeutic session and resulted in 90 to 100% occlusion in 83% of the lesions. Complications were encountered in 19% of the aneurysms. Rupture did not occur during any of the procedures. Clinical outcome was rated as GOS Score 5 or 4 in 83% of the patients and Grade 3 in 17%. During a cumulative clinical follow up of 821 years in 237 patients, 182 patients (81%) were independent (GOS Score 5 or 4), 33 (14%) were dependent (GOS Score 3), eight (3%) were in a vegetative state, and two (1%) had died. Clinical outcome was significantly worse after previous aneurysm rupture and following procedural complications. Conclusions. These results are within the range of published data for coil treatment of BA tip aneurysms and confirm both the safety and efficacy of this endovascular treatment method. KEY WORDS • aneurysm • endovascular treatment • coil occlusion • basilar artery tip • basilar artery bifurcation C J. Neurosurg. / Volume 103 / December, 2005 Abbreviations used in this paper: BA = basilar artery; GDC = Guglielmi detachable coil; GOS = Glasgow Outcome Scale; SAH = subarachnoid hemorrhage; SD = standard deviation; 3D = three-di- mensional.