perimesencephalic subarachnoid hemmorhage (PM-NASAH)

Q: What is perimesencephalic subarachnoid hemorrhage?

Answer: Perimesencephalic subarachnoid hemorrhage is a subtype of nonaneurysmal SAH (NASAH). It is not very common, but clinical identification is important as these patients usually have a benign course and do well. They may require different management strategies. These patients have a characteristic pattern of localized blood on computed tomography (CT) and have normal cerebral angiography. 

The initial clinical presentation may be the same, but rebleeding and vasospasm are less common. The efficacy of nimodipine is not very clear but is still a part of the standard of care.

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References:

1. Rinkel GJ, Wijdicks EF, Hasan D, et al. Outcome in patients with subarachnoid haemorrhage and negative angiography according to pattern of haemorrhage on computed tomography. Lancet 1991; 338:964.

2. Flaherty ML, Haverbusch M, Kissela B, et al. Perimesencephalic subarachnoid hemorrhage: incidence, risk factors, and outcome. J Stroke Cerebrovasc Dis 2005; 14:267.

3. Mensing LA, Vergouwen MDI, Laban KG, et al. Perimesencephalic Hemorrhage: A Review of Epidemiology, Risk Factors, Presumed Cause, Clinical Course, and Outcome. Stroke 2018; 49:1363.