Magnetic resonance imaging of subarachnoid hemorrhage

Computed tomography (CT) is the method of choice to detect acute subarachnoid hemorrhage (SAH). The sensitivity of CT has been reported to range from 85 to 100%. Magnetic resonance imaging (MRI) using FLAIR sequences shows a comparable sensitivity in acute SAH and in some cases can even be superior to CT. However, additional proton density weighted (PDW) TSE sequences or 3D-FLAIR sequences should be used to avoid false-positive results caused by flow artifacts. Conventional T 1 - or T 2 -weighted SE sequences or susceptibility weighted T 2 * or EPI sequences used for the diagnosis of intracerebral hemorrhage do not detect SAH reliably enough. In subacute SAH, starting from day 5 after the suspected hemorrhage, the sensitivity of MRI is clearly superior to CT. Patients with suspected ischemic stroke scheduled for the initial evaluation by MRI no longer need additional CT studies to rule out subarachnoid hemorrhage as long as the MRI protocols are adequate and the radiologist has the necessary experience.