Intraoperative evaluation of blood flow with indocyanine green videoangiography

Fluorescence angiography was first applied during neurosurgical procedures in the late 1960s by Feindel et al. [1], who used fluorescein to examine the anatomical aspects of the epicerebral circulation in five patients undergoing craniotomy and outlined the specific advantages during surgery for angiomas and aneurysms. Interestingly, they recognized the possibility for fluorescence angiography to identify the feeding arteries to an arteriovenous malformations (AVM), allowing for a planned resection [1]. Indocyanine green (ICG) fluorescence angiography was initially developed in ophthalmology to evaluate retinal microcirculation in a variety of disorders. Indocyanine green is a near-infrared fluorophore with absorption and emission peaks of 805 and 835 nm, respectively; it provides high-quality vascular images by using a special optical setup for near-infrared light [2]. After intravenous injection, ICG is bound to globulins within 2 seconds and remains intravascular when vessel permeability is normal [2]. It is not metabolized by the body and is excreted by the liver. There is no reabsorption by the intestine and no enterohepatic recirculation. It has a plasma half-life of 3-4 minutes [2]. Fluorescence angiography with ICG was first applied in neurosurgery in 2001 by Kuroiwa et al. [3], who evaluated venous sinuses and the course of superficial veins before dural opening by adding a filter adapted for the wavelength of ICG to a Zeiss surgical microscope [3]. Two years later, Raabe et al. reported the first standard use of ICG videoangiography during vascular procedures, mainly aneurysm clipping [2]. They suggested that the use of ICG videoangiography could influence surgical strategy, because they were able to evaluate the perfusion of the residual aneurysm and the patency of parent, branching, and small vessels (which were not visible with intraoperative digital subtraction angiography [DSA]) after clipping. However, they also recognized that the angiographic view was restricted to the angle of the surgical approach and that vessels covered by blood clots, aneurysm, or brain tissue could not be visualized.