The Modified Fisher CT rating scale: Grade 1 (minimal or diffuse thin SAH without IVH),indicating low risk for symptomatic vasospasm; Grade 2 (minimal or thin SAH with IVH) and Grade 3 (thick cisternal clot without IVH), indicating intermediate risk for symptomatic vasospasm; and Grade 4 (cisternal clot with IVH), indicating high risk for symptomatic vasospasm. Reproduced with permission from Claassen J, Bernardini GL, Kreiter K, Bates J, Du YE, Copeland D, Connolly ES Jr, Mayer SA: Effect of cisternal and ventricular blood on risk of delayed cerebral ischemia after subarachnoid hemorrhage: the Fisher scale revisited. Stroke 32:2012–2020, 2001. From: Frontera: Neurosurgery, Volume 59(1).July 2006.21–27