Intra-operative Fluorescence-based Visualisation of Blood Flow in Cerebrovascular Diseases
Intra-operative Fluorescence-based Visualisation of Blood Flow in Cerebrovascular Diseases
Intra-operative control of vessel patency and/or successful exclusion of vascular lesions are major goals in neurovascular procedures. Direct intra-operative inspection may fail.
Digital subtraction angiography is the gold standard for the diagnostic work-up of vascular lesions or vessel patency and can be used for a more detailed analysis, but it is a sophisticated and expensive procedure if performed intra-operatively. In the late 1960s, Feindel and co-workers presented their first results obtained from intra-operative evaluation of the vascular function of basal brain vessels and cerebral microcirculation using fluorescent dyes in patients undergoing neurosurgical procedures.5,6 Despite promising initial reports, fluorescence angiography failed to gain broad clinical acceptance among neurovascular surgeons; however, its integration into a compact system based on modern video technology and the use of a clinically well-tolerated fluorescent dye with few side effects – i.e. indocyanine green (ICG) – have prompted re-evaluation of this technique for neurovascular procedures.7
The original publication by Raabe et al. described excellent resolution with high image quality in illuminating arterial and venous vessels up to perforating arteries with a diameter of less than 0.5mm.7
One of the initial technical problems with the technique resulted from the construction of the commercially available IC-View device, in which the near-infrared laser was mounted on top of a video camera. The laser and the camera therefore had different optical axes and, in cases with a deep, narrow surgical field – such as basal brain arteries – vascular structures could be reached by only one of these optical axes, while the other axis was blocked by brain or other tissue. Combining the axis of the near-infrared laser with that of the video camera in the surgical microscope eliminated this technical limitation.8
When applied in 187 neurovascular surgical procedures, this technique of microscope-integrated, intra-operative, near-infrared ICG videoangiography showed good agreement with intra- or postoperative digital subtraction angiography in 90% of cases.8 It provided relevant information for the surgical procedure and led to modification of the surgical strategy or clip correction in up to 10% of cases.
However, it must be remembered that – in contrast to digital subtraction angiography – the ICG technique, even if microscope-integrated, depicts only superficial vascular structures that are not hidden behind brain tissue, aneurysm sacs or clips. Therefore, it is important to illuminate all vascular structures of interest during ICG videoangiography. When the contrast dye has been applied, the surgeon can still manipulate vascular structures such as a clipped aneurysm to detect residual filling of the aneurysm sac or neck. To judge equal flow in branching vessels, however, it is of the utmost importance to illuminate these vessels before injecting ICG to demonstrate simultaneous filling during the first passage of the fluorescent dye. This is because one problem with ICG videoangiography still awaits a solution: the technique is not capable of quantifying the blood flow rate within the visualised vessels, thus providing only binary information – i.e. ‘occluded’ or ‘patent’.
In contrast to the deep basal brain arteries approached in aneurysm surgery, it is much easier to illuminate and assess superficial cortical vessels by ICG videoangiography; its correspondence to post-operative digital subtraction angiography was 100% in a series of extra-intracranial bypass procedures.9
- Schmiedek P, Piepgras A, Leinsinger G, et al., Improvement of cerebrovascular reserve capacity by ec-ic arterial bypass surgery in patients with ica occlusion and hemodynamic cerebral ischemia, J Neurosurg, 1994;81:236–44.
- Sundt TM Jr, Siekert RG, Piepgras DG, et al., Bypass surgery for vascular disease of the carotid system, Mayo Clin Proc, 1976;51:677–92.
- Allcock JM, Drake CG, Postoperative angiography in cases of ruptured intracranial aneurysm, J Neurosurg, 1963;20:752–9.
- Feuerberg I, Lindquist C, Lindqvist M, Steiner L, Natural history of postoperative aneurysm rests, J Neurosurg, 1987;66:30–34.
- Feindel W, Yamamoto YL, Hodge P, The human cerebral microcirculation studied by intra-arterial radio-active tracers, coomassie blue and fluorescein dyes, Bibl Anat, 1967;9:220–24.
- Feindel W, Yamamoto YL, Hodge P, Intracarotid fluorescein angiography: A new method for examination of the epicerebral circulation in man, Can Med Assoc J, 1967;96:1–7.
- Raabe A, Beck J, Gerlach R, et al., Near-infrared indocyanine green video angiography: A new method for intraoperative assessment of vascular flow, Neurosurgery, 2003;52:132–9; discussion 139.
- Raabe A, Nakaji P, Beck J, et al., Prospective evaluation of surgical microscope-integrated intraoperative near-infrared indocyanine green videoangiography during aneurysm surgery, J Neurosurg, 2005;103:982–9.
- Woitzik J, Horn P, Vajkoczy P, Schmiedek P, Intraoperative control of extracranial-intracranial bypass patency by near-infrared indocyanine green videoangiography, J Neurosurg, 2005;102:692–8.
- Kuebler WM, Sckell A, Habler O, et al., Noninvasive measurement of regional cerebral blood flow by near-infrared spectroscopy and indocyanine green, J Cereb Blood Flow Metab, 1998;18:445–56.
- Woitzik J, Pena-Tapia PG, Schneider UC, et al., Cortical perfusion measurement by indocyaninegreen videoangiography in patients undergoing hemicraniectomy for malignant stroke, Stroke, 2006;37:1549–51.
