What is the perimesencephalic subarachnoid hemorrhage?

Answer: Perimesencephalic haemorrhage (PSH) is defined as confined bleeding in the cisterns around the mesencephalon, called: the cerebral aqueduct, tegmentum, the tectum, and the cerebral peduncles.

Explanation:

PSH has a probable incidence in patients with negative angiographies of around 50% to 75%. It is a pathology with no predominant age range, reported in all ages in the literature, including childhood. By definition, the condition corresponds to a tomographic finding of blood in the interpeduncular cistern that may extend to the other portions of the mesencephalon. This pathogenesis has not yet been completely clarified, but it is believed to come from a nonarterial source, assuming venous or capillary origin.