Among 1752 patients with aneurysm rupture from 3 series, 340 (19.4%; range, 15% 37%) had a history of a sudden severe headache before the event that led to admission.82,95,97 The importance of recognizing a warning leak cannot be overemphasized. Headache is a common presenting chief complaint in the emergency department, and aSAH accounts for only 1% of all headaches evaluated in the emergency department.92 Therefore, a high index of suspicion is war- ranted, because diagnosis of the warning leak or sentinel hemorrhage before a catastrophic rupture may be lifesaving.93 Seizures may occur in up to 20% of patients after aSAH, most commonly in the first 24 hours and more commonly in aSAH associated with intracerebral hemorrhage, hypertension, and middle cerebral and anterior communicating artery Noncontrast head CT remains the cornerstone of diagnosis of aSAH; since publication of the previous version of these guidelines,1,2 there have been only minor changes in imaging technology for this condition. The sensitivity of CT in the first 3 days after aSAH remains very high (close to 100%), after which it decreases moderately during the next few days.2,100 After 5 to 7 days, the rate of negative CT increases sharply, and lumbar puncture is often required to show xanthochromia. However, advances in magnetic resonance imaging of the brain, particularly the use of fluid-attenuated inversion recovery, proton density, diffusion-weighted imag- ing, and gradient echo sequences,101 103 can often allow the diagnosis of aSAH to be made when a head CT scan is negative and there is clinical suspicion of aSAH, possibly avoiding the need for lumbar puncture. 