Cerebral aneurysm: De novo genesis and rupture within 15 days.

We report the first case of de novo formation of a small 4- × 3-mm symptomatic aneurysm with subsequent subarachnoid haemorrhage (SAH) within 15 days. A pre-existing aneurysm was excluded by magnetic resonance angiography, as well as conventional angiography. In this case, there was no history of SAH, which is in contrast to other reported cases of de novo aneurysms that developed after previous aneurysm rupture.