In surgery for intracranial aneurysm, it is essential to confirm aneurysmal obliteration and the patency of parent and perforating arteries. Recently, intraoperative fluorescence video angiography has been widely used for this purpose.1-7 However, the observation field for this procedure has been limited to a microscopic view, and it has been difficult to confirm blood flow in areas obscured by skull base anatomy such as the clinoid process, cerebellar tentorium, parent arteries, and nerves. Consequently, the endoscope has been adopted for microsurgery to enable visualization of cerebral blood vessels in the dead angle areas of the microscope,8-12 but the endoscope cannot itself reveal real-time blood flow through the vessel walls. To overcome this problem, we adapted endoscopic indocyanine green (ICG) video angiography for cerebrovascular surgery and reported its efficacy for aneurysm surgery.13 However, this system and another commercial ICG endoscope system currently available require a diameter exceeding 4.0 mm to gain sufficient fluorescence, which makes it difficult to bring the endoscope into an appropriate position within the limited space available between eloquent areas.13-15 Therefore, the need arose to develop a small-caliber endoscope with a fluorescence video angiography system.
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