They can be. During an attack the blood supply to your brain cells is restricted which can lead to cell damage and depending on other risk factors, if your brain tissue is damaged it's called ischaemic stroke. And because the symptoms of a mini-stroke or transient ischemic attack (TIA) are so similar to a migraine attack, they can be mistaken as ‘just’ an aura symptom. The aura is possibly the most dangerous part of a migraine attack for these reasons.