Classic Case

Nonaneurysmal perimesencephalic SAH is not caused by trauma or aneurysmal rupture. This type of SAH, as opposed to aneurysmal SAH that presents a more diffuse spread of clots, typically shows localized blood clot located in the subarachnoid space around the midbrain and anterior to the pons (A and B, arrows). Diagnostic angiography such as CT angiography shows no aneurysms in the posterior circulation or top of the basilar artery (C, arrow). The SAH is often self-limited. Vasospasm is rare. It is probably secondary to venous hemorrhage.