Presentation
Sudden collapse. Non-verbal.
Patient Data
Extensive acute subarachnoid hemorrhage, moreso in the left sylvian fissure. There is a moderate degree of hydocephalus, which is expected..
Follow up CTA of the circle of Willis shows a bilobed outpouching from the posterior aspect of the left ICA terminus, most likely a posterior communicating aneurysm.
Case Discussion
Subarachnoid hemorrhage that is extensive and asymmetrically distributed should be treated as a ruptured aneurysm until proven otherwise. When no aneurysm is found following an extensive workup, sometimes with repeat CTA/DSA, we can consider perimesencephalic subarachnoid hemorrhage.