[A case of ruptured and unruptured developing cerebral aneurysms at the bilateral M2 bifurcations five years after surgery for ruptured aneurysm at the end of the azygos anterior cerebral artery].

A 36-year-old woman with 4 cerebral aneurysms at unusual sites including bilateral M2 bifurcation aneurysms is reported. She had been in good health in the previous 5 years since the treatment for a ruptured aneurysm at the end of the azygos anterior cerebral artery when she was 31 years old. Five years later, she became comatose with a huge hematoma in the right temporal lobe due to the rupture of the aneurysm at the right M2 bifurcation, which had been very small 5 years ago. She underwent an emergent clipping operation, and then she became alert with motor weakness extremities of on her left-side. Postoperative angiograms revealed a de novo aneurysm at the left M2 bifurcation and an aneurysm at the origin of the lenticulostriate artery, which has remained unchanged for 5 years. An aneurysm at the M2 bifurcation is rare, especially when it is situated bilaterally at the mirror sites. To detect de novo aneurysms, postoperative angiographical follow-up should be considered in patients with multiple aneurysms and in young patients.