Fig. 3

A Right middle cerebral artery (MCA) M2 bifurcation unruptured large aneurysm (20 × 18 mm, blue arrow) with two M3 branches starting from the aneurysm was diagnosed by computed tomography (a, b) and computed tomography angiography (c, d). During surgery, we exposed the aneurysm and performed electrocoagulation to shrink it (e). Then, conventional indocyanine green video angiography (ICG-VA) showed aneurysm (f, blue arrow), parent artery including M2 (red arrow) and two M3 (green arrows). FLOW 800 provided a color-coded map that displayed the brain vessels in contrasting colors depending on the fluorescence appearance after ICG injection (arteries: red, cortical capillaries: yellow/green, veins: blue) (g). After low flow extracranial-to-intracranial (EC-IC) bypass (superficial temporal artery-M3), we isolated and resected the aneurysm (h, i, blue arrow). Another ICG-VA (j) and FLOW 800 analysis (k) showed the aneurysm disappeared and the bypass vessel was unobstructed (blue arrow)