Diffusion-weighted and perfusion-weighted MR of cerebral vasospasm

With the development of acute efficacious means of treatment of subarachnoid haemorrhage by operative or endovascular means, it is important to prevent and monitor the occurrence of late events such as vasospasm. Indeed, cerebral vasospasm is the cause of delayed ischemic deterioration in a subset of patients with subarachnoid haemorrhage, Methods such as cerebral angiography or transcranial doppler sonography [15] have been used to demonstrate its presence. Functional studies have been performed with SPECT and PET [9] and MRI was primarily used as an anatomical correlate [10, 11] for late cerebral dysfunction. In order to be able to acutely assess and select the patients suspected of suffering from vasospasm ischemia, it is necessary to dispose of a sensitive and specific modality that is able to both detect acutely ischemia and to exclude other causes of brain dysfunction. Until recently, computed tomography was the modality of choice in acute ischemia: indeed not only were there initial concerns about the safety of performing MRI in patients with intracranial clips, but CT has been shown to be very reliable for the demonstration of acute bleeding (not only in cases of SAH, but also in cases of subdural and epidural hematomas). Conventional T2-weighted imaging of the brain, which is indeed very sensitive to edema, has also been shown to not be very capable of demonstrating ischemia in the hyperacute setting; the new modality should also be able to demonstrate changes within a therapeutic window beyond which therapeutic measures would be unsuccessful. However, new generations of aneurysm clips are allowed for use in MR imaging, making the investigation of vasospasm, possible.