There have been some studies in the literature that have shown migraines to be a predisposing risk factor for stroke in young adults, epsecially young women. The mechanism is not absolutely defined, but vascular instability (unstable vasodilation and constriction of the arteries in the brain) and possibly activation of the body's clotting system are thought to play a role. There are clinical syndromes such as CADASIL that include migraine and stroke as part of the syndrome. And there are some medications such as birth control pills and antimigraine meds that have been directly linked with strokes and headache. As for migraine and TIA specifically, the results of a recent Italian study did suggest that women under 35 who had migraines did have a higher risk of TIA than the normal population. Hope that helps.