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The first coil should be as thick, long, and large as possible. A retrospective study at the Toranomon Hospital revealed that if the volume of the first coil is 1/3rd or more of the total coil volume, there are less chances of retreatment. Thus, a thick and long first coil contributes to stable long-term anatomical results. The length of the first coil should be approximately 8% of the volume of the aneurysm. After the placement of the first coil, a smaller and shorter coil should be placed sufficiently close to it to complete the procedure. The goal is to achieve prevention of acute re-rupture in ruptured acute aneurysms and life-long prevention of rupture in unruptured asymptomatic aneurysms. If the coil does not detach, check the position of the detachment point, and replace the power supply. In addition, refer to the direction for use of the device for prevention of coil disconnection failure and countermeasures. Although it is not a recommended method, a method of rotating the delivery wire at the detached position to thread the coil and a method of reconstructing the electric circuit with a crocodile clip has been reported.

A 71-year-old woman was receiving dialysis for microscopic polyangiitis(MPA). She was transported to the emergency room after developing a headache and losing consciousness. She was in a coma and had dense left paralysis. Head computed tomography(CT)showed a subarachnoid hemorrhage. Head three-dimensional CT angiography showed an aneurysm proximal to the right M2(inferior trunk), which was considered as the source of bleeding. We performed an emergency aneurysm clipping surgery. However, we placed a permanent clip on the arterial wall defect when the clip detached from the parent artery. Pathological examination of the aneurysm revealed that the layered structure of the artery was damaged because of fibrin degeneration, suggesting that the aneurysm was caused by vasculitis. Coma persisted after surgery, and the patient was transferred to another hospital.We found only one report demonstrating an association between a cerebral aneurysm and MPA. Aneurysms resulting from vasculitis are common at the periphery, rather than at vessel bifurcations. Cyclic inflammatory activity causes progressive destruction of the blood vessel wall, further expanding the lumen and forming an aneurysm. Therefore, such aneurysms are more fragile than true aneurysms, and are more likely to be damaged or detached during surgery, as in the present case. Trapping of the parent artery should be considered when the aneurysm is damaged or detached. Accordingly, preoperative planning could anticipate the need for superficial temporal artery to middle cerebral artery bypass.