Origin of pretruncal nonaneurysmal subarachnoid hemorrhage: Ruptured vein,perforating artery, or intramural hematoma?

Pretruncal (perimesencephalic) nonaneurysmal subarachnoid hemorrhage (SAH) is a benign variant of SAH, Although angiography fails to show a source of the hemorrhage, mild basilar artery narrowing may be observed. The cause of pretruncal nonaneurysmal SAH has not been established. Recent imaging stud ies have demonstrated that the center of this type of SAH is not around the mesencephalon but is in the prepontine or interpeduncular cistern with the hemorrhage closely associated with the basilar artery. We review the possi ble sources of hemorrhage in these cisterns and hypothesize that pretruncal nonaneurysmal SAH is caused by a primary intramural hematoma of the basila r artery. Such an intramural hematoma would explain bleeding under low pres sure, the location of the hemorrhage anterior to the brainstem, and the typ ical findings of hemorrhage adjacent to the basilar artery lumen on magneti c resonance imaging and mild basilar artery narrowing on angiography, Altho ugh an intramural hematoma of the basilar artery would be easily identified at surgical exploration, such surgeries have never included the extensive base-of-the-skull approaches that are necessary to visualize the artery in the prepontine cistern.