<unk>  can be caused by a number of factors that narrow the<unk> <unk> es supplying the brain stem. It causes symptoms mainly because the brain stem does not get sufficient blood. The two<unk> <unk> es join to form a single<unk>  at the base of the brain. Usually, if one<unk><unk>  is not narrowed it will be sufficient to supply blood to the brainstem.
Vertebral artery disease
Vertebral artery dissection
Chiasmal Syndrome
Basal ganglia disease
Spinal cord tumor
Spinal tumor
Carotid artery stenosis
Spinal stenosis