In recent decades, an increasing number of neurosurgeons have realized the importance of venous preservation because injury to or occlusion of important intracranial venous structures might lead to severe complications, such as haematoma, epilepsy, cerebral oedema, hemiplegia, and aphasia [15]. Instead of depending heavily on their own surgical experience, neurosurgeons have taken advantage of neuroimaging tools such as DSA, MRA, MRV and TCD preoperatively to analyse the vascular structures surrounding the lesion. In addition, the development of intraoperative microvascular Doppler (MVD) and ICG-VA has made the visualization of intraoperative blood flow possible. These techniques help neurosurgeons understand the dynamic flow of the venous system and how to preserve them.
Groups of veins are treated differently after neurosurgeons make particular surgical judgements, involving the consideration of whether to preserve them [16]. The superficial cerebral veins are strongly interconnected, making it acceptable to sacrifice one of them. Additionally, once the terminal ends of the sylvian vein leave the fissure and enter the sphenobasal, sphenoparietal, or cavernous sinus, they can be safely sacrificed [17]. However, to avoid devastating consequences, including contralateral hemiplegia, bridging veins known as the central group of veins, should not be stretched, injured or sacrificed. Regarding the vein of Labbe, surgeons usually preserved it to avoid venous infarction of the temporal lobe at all costs. As injury to the deep venous system can lead to diencephalic oedema, hyperpyrexia and death, preservation of deep veins such as the vein of Galen is of great concern.[18,19,20,21] However, there are no clear guidelines for venous preservation, and it has been important to make surgical judgments on a case-by-case basis with the help of imaging tools.
In patients undergoing craniotomy for tumour resection, thrombosis of the cerebral veins and sinuses occurs from time to time. The symptoms have been highly variable, including headaches, seizures and delirium, which resulted in difficulties in providing a timely diagnosis [22]. When the infarcts are associated with increased intracranial pressure, patients might die because of cerebral herniation. To clarify the formation of vein thrombosis and deliver treatment as rapidly as possible, it has been important to use ICG-VA integrated with FLOW 800 during the surgical process. A preresection survey using ICG-VA integrated with FLOW 800 helped surgeons identify the pathophysiological changes in brain veins related to the tumour and individuate landmarks for the surgical approach, while a postresection survey, as demonstrated in our patients, helped surgeons confirm venous patency to reduce the risk of postoperative complications, including venous infarction and local hypoperfusion. Compared with conventional ICG-VA, the colour maps reconstructed by FLOW 800 software enables more intuitive cerebral blood flow monitoring. And the fluorescence intensity curve in ROIs with FLOW 800 allowed surgeons to study blood flow semiquantitatively in the same vein pre-and post-operatively.
As the first to report the use of microscope-integrated quantitative analysis of ICG-VA for blood flow assessment, Kamp et al. showed great value of the maps and promoted clinical applications of FLOW 800 analysis [6]. However, few articles have reported the use of ICG-VA along with FLOW 800, especially in the field of surgery for brain tumours, and cerebral and spinal haemangioblastomas [14, 23, 24]. In the present case reports, we described our experience with using ICG-VA integrated with FLOW 800 in brain tumour resection to observe venous flux and detect the obstruction of venous reflux in a timely manner. All of our patients had a good prognosis after surgery.
There were several limitations of our study. First, we included a small number of participants. Second, the use of ICG-VA with FLOW 800 was subjective based on the experience of the surgeon. We have not identified an optimal protocol for routine use throughout the procedure. In addition, quantitative data from FLOW 800 were not systematically collected and analysed. Furthermore, long-term follow-up investigations are needed.
A comparison between ICG-VA integrated with FLOW 800 and other techniques of blood flow monitoring such as MVD and intraoperative DSA is needed to demonstrate the sensitivity and specificity. We believe that the application of ICG-VA integrated with FLOW 800 will be expanded in the future.