This is called 'basilar-type' because it was first described in the areas of the brain which receive blood from the basilar artery, which includes most parts of the brain in the "posterior fossa" and also the brainstem, which are in the lower, back part of the brain (occipital region). But it was later seen that it may also affect areas of the brain outside of the areas which receive blood from the basilar artery. There is no proof that problems in the basilar artery are the cause.