• Alfredo Quiñones-Hinojosa and Michael T Lawton.
• Department of Neurological Surgery, Center for Stroke and Cerebrovascular Disease, University of California, San Francisco, San Francisco, California 94143-0112, USA.
• Neurosurgery. 2008 Jun 1; 62 (6 Suppl 3): 1442-9.

ObjectiveCerebral revascularization is an important part of the treatment of complex intracranial aneurysms that require deliberate occlusion of a parent artery. In situ bypass brings together intracranial donor and recipient arteries that lie parallel and in close proximity to one another rather than using an extracranial donor artery. An experience with in situ bypasses was retrospectively reviewed.MethodsThirteen aneurysms were treated with in situ bypasses between 1997 and 2004. During this time, 1071 aneurysms were treated microsurgically and 46 bypasses were performed as part of the aneurysm treatment.ResultsTreated aneurysms were located at the middle cerebral artery (MCA) in five patients, posteroinferior cerebellar artery (PICA) in three patients, vertebral artery in three patients, and anterior communicating artery in two patients. Seven aneurysms were fusiform or dolichoectatic, and six aneurysms were saccular. Microsurgical revascularization techniques included side-to-side anastomosis of intracranial arteries in eight patients and aneurysm excision with end-to-end reanastomosis of the parent artery in five patients. In situ bypasses included A3-A3 anterior cerebral artery bypass in two patients, anterior temporal artery-MCA bypass in one patient, MCA-MCA bypass in one patient, and PICA-PICA bypass in four patients. Aneurysm excision with arterial reanastomosis included three MCA aneurysms and two PICA aneurysms. On angiography, all aneurysms were completely obliterated and 12 bypasses were patent.ConclusionIn situ bypass is a safe and effective alternative to extracranial-intracranial bypasses and high-flow bypasses using saphenous vein or radial artery grafts. Although in situ bypasses are more demanding technically, they do not require harvesting a donor artery, can be accomplished with one anastomosis, and are less vulnerable to injury or occlusion.

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