Perimesencephalic subarachnoid hemorrhage: incidence, risk factors, and outcome.

Abstract in brief

• Perimesencephalic subarachnoid hemorrhage (PMSAH) accounts for about 5% of all nontraumatic subarachnoid hemorrhages and appears to have different causes and outcomes compared to aneurysm-related SAH, often involving hemorrhages restricted to specific brain regions and negative angiogram results.
• The study, based on a population in Greater Cincinnati, identified an incidence rate of roughly 0.5 per 100,000 people annually for PMSAH, with affected patients typically being younger, less likely to be female or hypertensive, and experiencing a generally good prognosis with only one death during follow-up.
• PMSAH's distinct risk factors and better outcomes suggest it is a separate clinical entity from other forms of SAH, emphasizing the importance of understanding its unique presentation and natural history.]