Clinical Study
Intraoperative near-infrared indocyanine green–videoangiography (ICG–VA) and graphic analysis of fluorescence intensity in cerebral aneurysm surgery

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Abstract

We present our preliminary experience with intraoperative near-infrared indocyanine green–videoangiography (ICG–VA) and analysis of blood flow dynamics using fluorescence intensity assessment in cerebral aneurysm clipping surgery. Thirty-nine patients with 43 intracranial aneurysms underwent microsurgical clipping. Intraoperative ICG–VA was performed before and after clip application. An infrared fluorescence module integrated into a surgical microscope was used to visualize fluorescence in the surgical field and we recorded the emitted fluorescent light. An integrated analytical visualization tool simultaneously analyzed the video sequence and converted it into an intensity diagram, which allowed an objective evaluation of the results rather than the subjective assessment of fluorescence using ICG–VA. Overall, ICG–VA was performed 137 times. Incomplete clipping was detected in four patients, which allowed suitable adjustment to completely obliterate the aneurysm. In 12 patients, perforators arising close to, or from, the aneurysmal neck were identified in the surgical field. In three patients, the ICG–VA intensity diagram provided valuable information leading to modification of the primary surgical maneuver. ICG–VA provides high resolution images allowing real-time assessment of the blood flow in the parent artery and arterial branches, including the perforators. The intensity diagram is useful for providing a more objective record of the hemodynamics than the traditional ICG–VA, which relies more on subjective assessment and may allow interobserver variability. We conclude that ICG–VA, combined with the intensity diagram, can reduce the morbidity and complications associated with aneurysm clipping and improve patient outcomes.

Introduction

The principle challenge in aneurysm surgery is to achieve complete obliteration of the sac while maintaining the patency of the parent artery, its nearby branches and any perforators. Following Raabe et al.’s report in 2003,1 several authors have recommended the use of indocyanine green videoangiography (ICG–VA) as an adjunct during intracranial aneurysm clipping.[2], [3], [4], [5], [6], [7] During intraoperative ICG–VA, neurosurgeons have relied on direct inspection of blood flow fluorescence to determine whether an aneurysm has been obliterated completely. To our knowledge, a microscope-integrated module that provides a record of fluorescence as an intensity diagram, in addition to the traditional near-infrared (NIR) ICG–VA, has not been evaluated. We present our experience with intraoperative ICG–VA and a graphic representation of fluorescence intensity to better understand the hemodynamics in cerebral aneurysm surgery. The clinical usefulness of this method is assessed.

Section snippets

Patient population

Thirty-nine consecutive patients (12 male, 27 female, mean age 61.1 years, range 31–78 years) underwent microsurgical clipping at our center between May 2010 and July 2010. A total of 43 intracranial aneurysms were clipped (7 ruptured, 36 unruptured). Ruptured intracranial aneurysms were categorized as Hunt and Hess (H&H) grade II in one patient, H&H grade III in three patients, and H&H grade IV in three patients. Of the 36 patients with unruptured aneurysms, four patients also had other

Results

We treated 43 aneurysms in 39 consecutive patients. Of these, 41 aneurysms were treated by clipping alone. Another two broad-neck, giant ICA aneurysms were treated by intentional reconstruction of the aneurysmal neck followed by endovascular coiling. None of the 41 aneurysms managed by clipping alone showed signs of major branch occlusion or residual aneurysm on the postoperative 3D–CTA.

ICG–VA was performed 137 times in 39 patients. The minimal interval between two consecutive procedures was 5

Discussion

ICG is an NIR fluorescent tri-carbocyanine dye used in medical diagnostics. The dye is injected intravenously, binds tightly to the plasma proteins and remains confined to the intravascular system. With a half-life of 3 minutes to 4 minutes, ICG is eliminated from the circulation into the bile exclusively via hepatic metabolism. Traditionally ICG has been used for evaluating cardiac output, hepatic function and in the assessment of blood flow across vascular anastomoses. ICG is also used widely

Conclusion

ICG–VA provides high resolution images and it allows a real-time assessment of the blood flow in the parent artery, arterial branches and adjacent small perforators. Interpretation of this information is, however, subjective. The intensity diagram is a very useful adjunct to ICG–VA for objectively documenting the blood flow in the aneurysm sac and perforators. This feedback is invaluable in optimizing the benefits and minimizing the complications during surgery for intracranial aneurysms.

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    The mechanism of uptake and secretion of ICG has been demonstrated to follow a saturable carrier-mediated transport process which can be described by the Michaelis–Menten equation [10,13,25]. Moreover, ICG has been widely used as clinical fluorescent dye, especially in angiographic diagnosis, due to its high contrast, sensitivity, safety, and low cost [26,27]. Yet, ICG does not have high fluorescence quantum yield (2.5% in water, 1.2% in blood), so a large part of the absorbed photon energy can be transferred to the non-radiative relaxation of molecules which can enhance photoacoustic wave generation after irradiation of short laser pulses [28].

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    Intraoperative angiography [13–16] and microscope-integrated indocyanine green video-angiography (ICG-VA) [17] are helpful tools in the surgical management of cerebral vascular malformations. Initially tested to help in intracranial aneurysms surgery [18–27] and to assess cerebral blood flow [28–31], ICG-VA has gained popularity also for its application in brain and spinal AVMs and arterio-venous fistulas [32–37]. Recently, positive experiences with ICG-VA during brain tumor surgery [38–40], resection of cerebral or spinal cord cavernous angiomas [41,42] and carotid endoarterectomy [43] have also been reported.

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    ICG is often compared to micro-doppler and digital subtraction angiography (DSA) to evaluate vascular anatomy, before and after clipping, and to assess correct position of the clip, presence of aneurysm residuals, patency of normal vessels. Few studies focused specifically on paraclinoid aneurysms [10,19] and on quantitative blood flow study [7,12,18](which allows an objective evaluation of the results rather than the subjective assessment of fluorescence using ICG-VA). One interesting paper reports about a patient suffering from a giant aneurysm of the right MCA; Indocyanine green was injected inside the aneurysm in order to identify a target middle cerebral artery branch (MCA) for bypass and allowing confident preservation of blood supply to distal areas to the sacrificed vessel [11].

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