Perimesencephalic nonaneurysmal subarachnoid haemorrhage and variations in the veins.

Perimesencephalic nonaneurysmal subarachnoid haemorrhage (PN-SAH) is characterised by accumulation of blood around the midbrain, normal angiographic findings and an excellent prognosis. The etiology of PN-SAH has not yet been determined. Therefore we decided to compare the venograms of patients with PN-SAH with those of patients with aneurysmal SAH (A-SAH) in order to examine the relationship between PN-SAH and venous structures. We retrospectively studied 6 patients with PN-SAH and 102 cases of angiographically evaluated A-SAH during the past 12 years by reviewing their venograms for possible abnormalities in venous structures, particularly in the basal vein of Rosenthal (BVR). More abnormalities in venous structures were found in the patients with PN-SAH than in those with A-SAH. Most of the BVR in the patients with PN-SAH appeared to drain into various dural sinuses instead of the galenic system. The relationship between PN-SAH and abnormalities in venous structures was determined.