Headaches associated with vascular disorders in the IHS Classification is category 6.0 (Table 1). Sudden, severe, "blinding", excruciating headache, with stiff neck, vomiting, and altered mental status, is the classic presentation for ruptured berry aneurysm. Subarachnoid blood is usually found on lumbar puncture, if it is performed, and the majority of CT scans reveal evidence of blood. Focal neurologic deficits may occur following rupture of berry aneurysms, such as the third nerve palsy that often follows rupture of a posterior communicating artery aneurysm or hemiparesis following middle cerebral artery aneurysm rupture. The syndrome of "occipital apoplexy": sudden headache, stiff neck and a homonymous field defect is almost pathognomonic for a ruptured occipital lobe AVM.6 Any patient, with sudden severe headache, with or without stiff neck or focal neurologic signs must be evaluated with the possibility of ruptured or unruptured vascular anomaly such as aneurysm or AVM. The other neuro-ophthalmologic signs and symptoms of aneurysms, AVMs, and related vascular anomalies are detailed in another chapter. Unruptured aneurysms and AVMs may also produce headache. When the headache pattern is completely stereotyped throughout life, strong suspicion should be raised as to the possibility of an arteriovenous malformation rather than migraine with aura.50 Sentinel headaches are reported to occur in about 50 percent of patients days to weeks preceding subarachnoid hemorrhage from berry aneurysm.{47} About half such headaches are reported to be abrupt in onset and severe and have been believed to be due to an initial leak due to partial rupture. Such patients should probably be evaluated with arteriography even if the cerebrospinal fluid does not disclose blood as Day and Raskin{202} have documented that thunderclap headache episodes may occur as symptoms of an unruptured aneurysm.