From what I understand, strokes are caused by the same thing heart attacks are - atherosclerotic plaques, and APs are caused by high blood cholesterol - APs are literally constituted of cholesterol/foam cells. Has the consensus changed?
Anecdata: My dad died of a hemorrhagic stroke. My mom of an occlusive stroke. No plaques in my dad. A very few in my mom. It's complicated.
Interestingly, dissections as you mention cause ischemic strokes by (generally speaking) flicking off clots that mess things up downstream that form within a pouch made by the dissection (low blood flow + body trying to patch things up = pro-coagulation). Note in this case there is a tear in the artery wall but the wall remains (ie, no blood exits the artery).
This is different than an aneurysm, when the arterial wall bursts and you have bleeding within the brain. That is termed a hemorrhagic stroke.
Source: hospitalist physician for 7 years who has cared for 100s of strokes at a hospital that specializes in neurology.