Narrowing of the lumen of one or more intracranial arteries due to contraction of arterial smooth muscle or to morphologic changes of the blood vessel wall. Large blood vessels near the base of the brain are primarily affected and reduced blood flow may result in hypoxic-ischemic brain injury (HYPOXIA-ISCHEMIA, BRAIN). Vasospasm may be associated with SUBARACHNOID HEMORRHAGE; $CRANIOCEREBRAL TRAUMA$; and other disorders. (From Neurosurg Clin N Am, 1998 Jul;9(3):615-27).