Acute diagnostic workup should include noncontrast head CT, which, if nondiagnostic, should be followed by lumbar puncture (Class I; Level of Evidence B). 3. CTA may be considered in the workup of aSAH. If an aneurysm is detected by CTA, this study may help guide the decision for type of aneurysm repair, but if CTA is inconclusive, DSA is still recommended (except possibly in the instance of classic perimesen- cephalic aSAH) (Class IIb; Level of Evidence C). (New recommendation) 4. Magnetic resonance imaging (fluid-attenuated inver- sion recovery, proton density, diffusion-weighted imaging, and gradient echo sequences) may be rea- sonable for the diagnosis of aSAH in patients with a nondiagnostic CT scan, although a negative result Connolly et al Management of Aneurysmal Subarachnoid Hemorrhage 1719 does not obviate the need for cerebrospinal fluid analysis (Class IIb; Level of Evidence C). (New recommendation) 5. DSA with 3-dimensional rotational angiography is indicated for detection of aneurysm in patients with aSAH (except when the aneurysm was previ- ously diagnosed by a noninvasive angiogram) and for planning treatment (to determine whether an aneurysm is amenable to coiling or to expedite microsurgery) (Class I; Level of Evidence B). (New recommendation) Medical Measures to Prevent Rebleeding After aSAH Aneurysm rebleeding is associated with very high mortality and poor prognosis for functional recovery in survivors. 