We report a case of 74-year-old man with a recurrent subarachnoid hemorrhage (SAH) caused by a de novo aneurysm. He suffered from SAH due to a ruptured aneurysm at right middle cerebral artery (MCA) bifurcation and had a neck clipping surgery of the aneurysm. At that time a 4-vessel-angiography revealed no aneurysm at left MCA. One year and 2 months after a clipping, he suffered from cerebral infarction and underwent an angiography again. The second angiography showed a small bulge at left MCA. But we could not recognize it at that time. He suffered from recurrent SAH about 16 months after the first episode. The third angiography revealed a distinct aneurysm at left MCA trifurcation. The aneurysm had newly developed within only 1 year and 2 months and rapidly grown up to rupture for 6 weeks. In this case we recognized hypertension and cigarette smoking as risk factors of de novo aneurysm, and the de novo aneurysm developed at a mirror site, a common site of de novo aneurysm. It is very important for patients with a prior SAH to manage these risk factors.
