To describe the technical integration of indocyanine green (ICG) near-infrared technology into the optical path of the surgical microscope and to report on the image quality achieved by this method. We hypothesized that ICG angiography permits a simple and quick intraoperative assessment of vessel patency and aneurysm occlusion after clip placement.

A special arrangement of filters was designed to allow the passage of near-infrared light required for the excitation of ICG fluorescence (700-850 nm) from a modified microscope light source into the surgical field and the passage of ICG fluorescence (780-950 nm) from the surgical field back into the optical path of the surgical microscope (Carl Zeiss, Oberkochen, Germany). Thus, ICG angiography could be completely performed with a surgical microscope. 20 patients with intracranial aneurysms were included in the technical evaluation of the new method.

Image quality and spatial resolution were excellent and permitted a real-time assessment of vessel patency and aneurysm occlusion if the structures of interest were visible to the surgeon’s eye under the microscope, including perforating arteries with a diameter of less than 1 millimeter. In 1 patient, vessel occlusion by the clip was found and in 1 case residual filling of the aneurysm was diagnosed. Both cases could be treated by clip correction within 2 minutes after primary placement of the clip. In all cases, the intraoperative findings correlated with the postoperative digital subtraction angiography.

ICG angiography using a surgical microscope is valuable for the intraoperative imaging of arterial and venous flow in all visible vessels including small perforating arteries. The simplicity of the method and the speed with which the investigation can be performed indicate that this technique may help to improve the quality and outcome of surgical procedures and reduce the need for intra- or postoperative angiography in selected cases.