Giant, partially thrombosed aneurysm develops after remote angiographically negative subarachnoid hemorrhage: case report.

Objective: This is the first report of the rupture of a giant aneurysm in a patient who sustained a remote angiographically negative subarachnoid hemorrhage (SAH).

Clinical Presentation: A 62-year old woman initially presented with a Fisher Grade III SAH 9 years ago. Her evaluation, which included cerebral angiography, magnetic resonance imaging scans, and magnetic resonance angiography of the head and neck, failed to reveal the cause of the hemorrhage. Nine years after her initial hemorrhage, the patient presented with a Fisher Grade IV SAH and a giant right supraclinoid internal carotid artery aneurysm.

Intervention: Computed tomographic and catheter angiography showed a partially thrombosed giant aneurysm of the right supraclinoid internal carotid artery. She underwent clip reconstruction and obliteration of the aneurysm. Review of her previous angiograms and magnetic resonance imaging scans did not show an aneurysm in its nascency.

Conclusion: Initial catheter angiography and magnetic resonance imaging scans may fail to disclose a subtle dissection or blister aneurysm as a cause for SAH. As in our case, the dissection or blister may progress to a giant aneurysm with time.