Staged surgery for a large cerebral arteriovenous malformation to prevent the overload phenomenon

Intracerebral hemorrhage and/or edema is a sequel following removal of a large nidus. We call the vascular load an 'overload phenomenon'. To prevent it by stepwise reduction of the nidus size, staged surgery is recommended for a large AVM (nidus size of more than 5 cm). With the recent advancement of the intravascular technique, preoperative embolization is also a good option to reduce the nidus size resulting in a prevention of the overload phenomenon and a reduction in intraoperative bleeding. The overload phenomenon is visualized on the immediate postoperative angiogram as 'modja-modja' (stagnating and shaggy) vessels around the removed nidus, which disappear in a month. We present a case in which those vessels were identified. Maintaining the postoperative blood pressure at 80 to 100 mmHg is also essential for preventing the overload phenomenon prior to staged surgery and/or preoperative embolization.