Perfusion-diffusion mismatch in MRI to indicate endovascular treatment of cerebral vasospasm after subarachnoid haemorrhage
Endovascular treatments such as transluminal balloon angioplasty and intra-arterial nimodipine represent rescue therapy for cerebral vasospasm (CVS) after aneurysmal subarachnoid haemorrhage (SAH). Both indication and data regarding its efficacy in the prevention of cerebral infarct are, however, inconsistent. Therefore, an MR based perfusion weighted imaging/diffusion weighted imaging (PWI/DWI) mismatch was used to indicate this treatment and to characterise its effectiveness.
MRI was performed for suspicion of CVS. For quantitative evaluation, the brain was partitioned into 19 arbitrary segments of comparable volume. Segments with PWI/DWI mismatch were defined as ‘segment at risk (SR)’. In these cases, MRI was followed by angiography (digital subtraction angiography (DSA)) including endovascular treatment. 48±12 h after treatment, a second MRI was performed and the treatment was repeated if new or remaining SR were observed. Efficacy was classified as the percentage of reduced diameter of the proximal cerebral arteries on DSA following the treatment: mild (≥33%), moderate (34–66%) or severe (≥67%).
48 treatment cycles, each consisting of MRI, DSA and a second MRI, were performed in 25 patients. During these cycles, 95 SR were identified. The infarct rate was significantly higher in SR (37%) compared with segments without risk (4%). The infarct rate in SR was significantly reduced if mild proximal CVS could be achieved. In the case of persistent severe CVS, infarcts occurred in all SR.
The present series suggests that PWI/DWI mismatch is predictive of the development of infarct in the case of CVS. The infarct rate could, however, be improved if proximal CVS was sufficiently reduced.