Understanding the hemodynamics and angioarchitecture is essential in HGB surgery. HGB are characterized by tumor hypervascularity. Thus, surgical resection harbors the risk of significant blood loss and surgical complications [1, 8, 9]. Conventional angiography, computed tomography angiography, or magnetic resonance angiography are usually performed to evaluate the angioarchitecture of HGB . However, real-time vascular imaging is more helpful during tumor resection. Doppler ultrasonography (US) has been used for distinguishing arteries and veins of tumors. Doppler US has also the advantage of being non-invasive and straightforward to apply for evaluating vessels. However, Doppler US is less reliable for small arteries and low-flow tumor vessels and it cannot visualize tumors, vessels, and the direction of blood flow. Since recently, ICG angiography is widely used in cerebrovascular surgery , and it may also have potential for brain tumor surgery. The results of ICG angiography are easy to interpret to determine the angioarchitecture of HGB tumors. In addition, ICG infusion is a safe procedure and can be performed repeatedly. Kim et al. reported various applications of ICG angiography for brain tumor surgery  and shared their experience using ICG angiography for various types of brain tumors. HGB tumors show bright staining in ICG angiography [5, 7]. Moreover, ICG angiography can reveal the feeding arteries, draining veins, and the direction of flow. Thus, ICG angiography is a more useful adjunctive tool than Doppler US in HGB resection.
The morphology of HGB is heterogeneous and HGB are frequently accompanied by tumor cysts, making tumor resection potentially challenging. Identifying small mural nodules in the large cyst is difficult via gross microscopic inspection but is easy via the ICG microscopy mode. In addition, using bright tumor staining by ICG may be used to confirm the total resection of HGB tumors.
Assessing feeding arteries and draining veins is important in HGB surgery because coagulation of feeding arteries reduces bleeding during surgery. Minimizing blood loss can reduce the need for blood transfusion, helps with rapid recovery of patients, and overall reduces the cost of hospitalization. In addition, because ICG fluorescence can penetrate the dura mater, ICG is useful to assess cortical vessels and trans-dural feeders before dura opening .
Large solid HGB tumors can mimic arteriovenous malformation, showing numerous feeding arteries and large draining veins [9, 10]. These large tumors can harbor tumor-related arteriovenous shunts. Premature occlusion of shunts without adequate feeding arteries causes devastating bleeding which can put the entire surgical procedure at risk. ICG angiography is useful for assessing shunt flow and direction of blood flow, and can help identifying the residual feeders after subcortical dissection of the tumor.
In our experience, ICG angiography is very useful during HGB surgery. The purposes of ICG angiography are listed below.
<The purposes of ICG angiography>
Identifying small tumors inside of tumor cysts
Identifying tumors that are located in subcortical areas
Defining feeding arteries and draining veins
Confirming extent of resection, residual tumor tissue
Assessing tumor-related arteriovenous shunt flow
The limitation of ICG angiography is that it is available only for vessels visible in the operative field. It cannot visualize vessels and tumors which are covered with brain parenchyma. Weak staining of tumor tissue just beneath the cortex and dura mater could be seen but deeper-seated tumors could not be visualized. Although the incidence is extremely low, anaphylactic reactions such as itching sensation, skin eruption, arrhythmia, and hypotension have been reported after ICG administration . These side effects should be discussed preoperatively.