[Indirect Revascularization Surgery for Chronic Ischemia in Moyamoya Disease]

Indirect revascularization is a surgical procedure to reduce cerebral ischemia, using subcutaneous tissues or dura mater supplied by extracranial arteries as grafts. The perfusion pressure gradient between the cortex and the graft, if present, induces arteriogenesis and develops extracranial-intracranial anastomoses to supply blood flow to the cerebral cortex underneath the graft. Therefore, it is essential to perform the craniotomy over the site of the cerebral ischemia to induce functional anastomoses. The details of the indirect revascularization procedure vary among institutes in terms of the grafts used(skin arteries, such as the superficial temporal artery; temporal muscle, galea, or pericranium), dura mater incisions(removal and replacement with the grafts, linear incision, or multiple small incisions), and the location and size of the craniotomy. Indirect revascularization is especially effective in patients with moyamoya disease because the pathophysiology of the disease itself is related to intracranial to extracranial carotid system conversion. Generally, indirect revascularization was considered ineffective in patients with atherosclerotic steno-occlusive cerebrovascular disease; however, recent clinical trials suggested that it may also be effective in these patients. If a future clinical trial demonstrates a positive outcome, indirect revascularization may become a possible treatment for atherosclerotic patients.