[De novo aneurysm after ten days from the onset of SAH].

A 56-year-old man presented with severe headache. Neurological examinations found no abnormalities and no disturbance of consciousness. CT revealed a subarachnoid hemorrhage. DSA showed an aneurysm located at the junction of the right internal carotid artery and the anterior choroidal artery. Next day, neck clipping was performed. The aneurysm adhered to the temporal lobe, and it seemed without doubt that it was a ruptured aneurysm. On day 10, we performed a carotid angiography on schedule. DSA revealed a newly arisen aneurysm originating from the middle cerebral artery close to the origin of the lenticulostriate artery and a vasospasm in the internal carotid artery and the middle cerebral artery. On day 14, we again performed surgery. The aneurysm was embedded in the insular cortex, but it seemed to be a non-ruptured aneurysm. After surgery, the patient had no apparent neurological deficits, and he returned to normal daily life. De novo aneurysms have been discovered after at least a few years. This case is very rare because the aneurysmal formation is of much a short interval.