Don't take this the wrong way but your statement is incorrect. I don't have time to type out all the various subsets of strokes but Wikipedia is a good initial source. Dissections are fairly uncommon. Far more common are emboli strokes from afib, small vessel atherosclerosis, for example.

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.