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Background: Perimesencephalic nonaneurysmal hemorrhage is a benign form of subarachnoid hemorrhage with a low risk of rebleeding. The authors conducted a retrospective study to investigate the prognosis, possible prognostic factors, and long-term natural history in perimesencephalic nonaneurysmal subarachnoid hemorrhage (PNSH)., Methods: This report contains a retrospective analysis of 29 patients with PNSH who were followed from 1 month to 8 years with an average follow-up period of 5.4 years. We evaluated computed tomography (CT) scan features; clinical grade; loss of consciousness during hemorrhage; ventricular ratio; angiographic spasm; complications such as ischemic complications, early rebleeding, late rebleeding, epilepsy, hydrocephalus, and fixed ischemic deficit; and outcome., Results: There were 7 men and 22 women, and the ages ranged from 22 to 69 years (mean 49.5 years). In the group with PNSH 93% of the patients were in grade I-II, as compared to 70.8% of patients with non-PNSH according to the Hunt and Hess system. Loss of consciousness during hemorrhage was detected in 9 patients (31%). We observed acute hydrocephalus in 4 patients (13.7%). The first cerebral four-vessel angiograms disclosed vasospasm in 3 patients (10.3%). Patients with PNSH have the best outcome according to the activities of daily living (ADL) grading system when compared with other groups of patients with negative angiogram (aneurysmal pattern and invisible blood)., Conclusion: This study provides evidence that patients with PNSH have an uncomplicated course and a particularly favorable outcome.

Cerebral vasospasm is one of the most important factors influencing morbidity and mortality of intracranial operations or diseases. Platelet aggregation and adhesion is increased in spastic vessels. Degradation of platelets liberates mediators, which in turn increase vasospasm, thus creating a vicious cycle. Healthy vessels cope with this by increasing the synthesis of prostacyclin. The purpose of this study was to increase experimentally the levels of arterial prostacyclin and adenosine triphosphate (ATP) in animals through intraarterial injection of these substances because they are lower in spastic vessels. Prostacyclin promotes antiaggregation and dilatation, increases blood flow, inhibits thromboxane A2, and prevents synthesis of angiotensin II. Most of these effects were done by increasing cyclic adenosine monophosphate (cAMP). After injecting autogenous blood into the cisterna magna of male dogs, both the acute and chronic phases of vasospasm and the degenerative changes in the arterial wall were observed. Injecting ATP increased the severity of vasospasm. During vasospasm it was found that when prostacyclin is used intraarterially, vasodilatation began, but degeneration of the arterial wall could not be prevented. In the group of animals in which both ATP and prostacyclin were used, there was no degeneration of the arterial wall and the basilar artery was seen to be normal when viewed under the electron microscope.