Along our theme of basilar perforator “nonaneurysmal” SAH — except that there is an aneurysm. Prognosis generally excellent so conservative management is first choice with us. The point is perimesencephalic spectrum hemorrhages are not “venous” — they are arterial perforator aneurysms. Why not both etiologies? Because why would a totally different and invisible cause (venous) cause an identical pattern of hemorrhage as that seen with actual arterial perforator aneurysms. The more likely scenario is that some small aneurysms thrombose / close before angio or are below resolution. Here is a big one — hemorrhage is much more then “perimesencephalic” — but that’s a spectrum also

Need good quality images to see them — even a big one like this. Can be seen here

Better reconstructions are better. Pretty large thalamoperforator here…