Fig. 1

A left internal carotid artery (ICA) C4 segment unruptured giant aneurysm (25 × 20 mm, blue arrow) with carotid-cavernous fistula (CCF, green arrow) was diagnosed by computed tomography (a), computed tomography angiography (b), digital subtraction angiography (c), and 3-dimensional rotational angiography (d). During surgery, the aneurysm was exposed (e). Then, conventional indocyanine green video angiography (ICG-VA) showed aneurysm (f, blue arrow), parent artery, and peripheral blood vessels. 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 high flow extracranial-to-intracranial (EC-IC) bypass (middle cerebral artery M3 segment-radial artery-ICA), we isolated aneurysm at ICA initial part and ICA before posterior communicating artery (PComA) branching (h). Another ICG-VA (I) and FLOW 800 analysis (j) showed the aneurysm disappeared (blue arrow) and the bypass vessel was fluent (green arrow)