Q: What is Perimesencephalic nonaneurysmal subarachnoid hemorrhage (PM-NASAH)?


Answer:  Perimesencephalic nonaneurysmal subarachnoid hemorrhage (PM-NASAH) is a subtype of subarachnoid hemorrhage (SAH) patients with pattern of 

• localized blood on CT scan of head 
• normal cerebral angiography, and 
•  usually a benign clinical course 

It presents as severe headache and should be managed in a similar fashion till PM-NASAH is established. In most cases the etiology remains undetermined. 



Reference: 

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