Indocyanine Green Videoangiography and Arteriovenous Malformations

19 Indocyanine Green Videoangiography and Arteriovenous Malformations


Justin R. Mascitelli, Jan-Karl Burkhardt, and Michael T. Lawton


Abstract
Indocyanine green videoangiography (ICG-VA) is a useful intraoperative tool for outlining the anatomy and assessing extent of resection of intracranial arteriovenous malformations (AVMs). ICG is a dye that can be injected intravenously and then can be seen with the operative microscope using an optical filter that allows only fluorescence in the ICG emission wavelength to pass through and be detected by infrared cameras. ICG-VA can be performed prior to, during, and following AVM resection. Benefits include safety, ease of use, and ability to distinguish AVM vessels from normal vessels. Limitations include that it can only visualize vessels that can be seen directly by the microscope and therefore poorly visualizes obscured anatomy, deep lesions, and deep venous drainage, as well as vessels covered by brain parenchyma or hematoma. In a published series, postresection ICG-VA fails to identify residual AVM in up to 12.5% of cases. Therefore, ICG-VA should be used as an adjunct to, but not as a replacement of, intraoperative or postoperative digital subtraction angiography. FLOW 800 software provides quantitative measurements of flow and may enhance ICG-VA during intracranial AVM resection, but has not been proven to impact intraoperative decision-making or patient outcome. ICG-VA is also particularly useful in the treatment of intracranial and spinal dural arteriovenous fistulas, in which the dye can readily identify the fistulous point and subsequent disconnection.


Keywords: indocyanine green videoangiography, arteriovenous malformation, arteriovenous fistula, fluorescence


19.1 Introduction


The goal of cerebral arteriovenous malformation (AVM) surgery is complete AVM resection with preservation of normal vascular and neural tissue. Accomplishing this goal, however, can be quite challenging. AVMs can abut or frankly involve eloquent brain tissue, they frequently receive arterial supply from en passage arteries that go on to supply vital brain structures, and their complete obliteration is not always obvious to the naked eye. Throughout AVM surgery, the surgeon is constantly walking the fine line between the AVM and normal brain structures. Inevitably, this delicate balance translates to a percentage of incomplete AVM resections.


The postoperative digital subtraction angiogram (DSA) is the gold standard for assessing the extent of AVM resection. This test, however, is performed after the surgery has been completed and, in turn, after there is an opportunity to resect residual AVM, if present. To address this problem, a number of intraoperative techniques have been developed over time to assess the extent of resection well before the postoperative angiogram and allow the surgeon to perform further resection, if needed, without having to perform a second operation. These techniques include the use of microvascular Doppler and flow probe measurements, intraoperative DSA, and indocyanine green videoangiography (ICG-VA).


19.2 Intraoperative Digital Subtraction Angiography


Intraoperative DSA has been used since the 1960s during cerebrovascular surgery1,2 and is the standard by which all other intraoperative modalities are assessed. Despite its long-standing use, its routine application has been debated. Issues such as safety, efficacy, and practicality have been brought into question. Additionally, its usefulness has also been reconsidered given the more widespread use of ICG videoangiography as well as the trend of more complex cerebrovascular cases being treated by endovascular means. In a review of over 1,000 patients undergoing cerebrovascular surgery, including over 100 patients undergoing AVM resection, Chalouhi et al found that complications were all minor and transient and occurred in less than 1% of cases.3 In this series, the rate of detection of residual AVM by intraoperative DSA was 9.8%, which falls in the previously reported range of 3.7 to 27.3%.4 The practicality of using intraoperative DSA is institution specific. Certain drawbacks include the need for an interventional radiologist (if the neurosurgeon performing the surgery is not dual trained), poorer quality images using a mobile fluoroscopic unit, and increased operative time. Increased availability of hybrid operating rooms has the potential to mitigate the practicality issue.5


19.3 Indocyanine Green Videoangiography


ICG is a fluorescent molecule that can be used to view the cerebral vasculature. The dye is administered via a peripheral venous line by the anesthesiologist (typically 25 mg in 10 mL of saline) and can be seen within the cerebral arteries 3 to 12 seconds after injection. Intra-arterial administration of ICG has also been described, but is not the common route.6 After administration, the molecule is immediately bound by globulins and remains in the intravascular space until excretion by the liver. It has absorption and emission peaks of 805 and 835 nm, respectively. The microscope records in real time with an optical filter that allows only fluorescence in the ICG emission wavelength. The dye rapidly passes into capillaries and then veins. Arterialized veins fluoresce in the late arterial phase. Therefore, the ICG-VA can be used to assess both physiological and pathological states, such as cerebral AVMs. Importantly, only vessels in the operative field that are directly visible by the microscope will be visualized with ICG-VA.4


Fluorescence-based angiography has been used for decades to assess the retinal vasculature during ophthalmological procedures. Although the use of fluorescence for viewing cerebral vasculature was reported as early as the 1960s,7 the application of ICG-VA was first introduced into neurosurgery in the early 2000s.8,9 ICG-VA was first employed during aneurysm10 and bypass surgery,11 and then subsequently in AVM surgery.4


19.3.1 Indocyanine Green Videoangiography for Intracranial AVMs


ICG-VA can be performed prior to, during, and following AVM resection. Typically, the dye is injected once the dura is open and vessels directly visualized. It can be performed prior to dural opening, however, to help visualize vessels through the dura and improve the safety of dural opening.12 ICG-VA can be performed before, during, and after AVM resection and is most useful for superficial AVMs with anatomy that can be directly viewed (image Fig. 19.1 and image Fig. 19.2; Video 19.1). The initial ICG-VA should focus on fully understanding the AVM anatomy by identifying feeding arteries, nidal arteries, and draining veins. The surgeon must distinguish pathological and normal vessels (image Fig. 19.3), which may include primary and secondary veins, terminal feeding arteries, transit (or en passage) arteries, and bystander arteries.13 Special attention should be paid to protecting the primary draining vein as well as identifying and preserving transit and bystander arteries, both of which go on to supply normal brain. Visualization of deep vessels (deep veins, perforating arteries, and choroidal feeding arteries) will frequently not be possible with the initial ICG-VA as the AVM nidus and normal parenchyma will block the line of sight to these deep vessels (image Fig. 19.4).


image Table 19.1 summarizes the available series evaluating traditional ICG-VA for AVMs (not using FLOW 800 software, which is discussed later).4,14,15,16,17,18,19,20 In 2009, Killory et al published the first series utilizing ICG angiography for 10 patients with intracranial AVMs.4 The authors found it useful in 9 of 10 patients. Two patients had residual AVM on intraoperative DSA, one of which had an ICG-VA that was deemed negative at the time but positive in retrospect. ICG also helped identify a small residual nidus within a hematoma. The authors concluded that the limitations of ICG-VA use are deep-seated lesions or when AVM vessels are not on the surface. Hänggi et al reported its use in 17 patients (15 AVMs and 2 arteriovenous fistulas [AVFs]).14 The surgical strategy was changed in two cases based on ICG findings. One patient had a false-negative ICG-VA that failed to demonstrate a small residual nidus that was seen on the postoperative DSA. Bilbao et al reported 37 patients with AVMs and compared ICG-VA to both intraoperative and postoperative DSA.18 Residual AVM was identified on intraoperative DSA in two patients and postoperative DSA in one patient. The authors concluded that ICG-VA should only be used as an adjunct and that deep/high-grade AVMs were the most difficult to visualize.



Feb 12, 2020 | Posted by in NEUROSURGERY | Comments Off on Indocyanine Green Videoangiography and Arteriovenous Malformations
Premium Wordpress Themes by UFO Themes