[Cerebral perfusion computerized tomography in vasospasm after subarachnoid hemorrhage: diagnostic value of MTT].

PURPOSE: Analysis of the value of the perfusion parameter mean transit time (MTT) for the diagnosis of cerebral vasospasm after Subarachnoid Hemorrhage (SAH). Comparison with other perfusion parameters. An MTT threshold indicating the necessity of conventional angiography will be defined.
MATERIALS AND METHODS: We analyzed the CT Perfusion (CTP) of 20 patients suffering from SAH (Fisher grading 3 and 4). In each patient a baseline examination was performed the day after treatment of the ruptured aneurysm. Follow-up was indicated for the occurrence of clinical symptoms, pathologic Doppler values or the first day after endovascular therapy. The cortical mean transit time (MTT), T (max,) cerebral blood flow (CBF) and cerebral blood volume (CBV) were calculated. A vasospasm score resulting from the Doppler values and clinical neurological symptoms was compared to MTT in the follow-up. The outcome after discharge from the intensive care unit was compared to the maximum MTT.
RESULTS: 18 patients were able to be evaluated. We found parallelism between the time course of MTT and clinical symptoms in 14 of 18 patients. In 4 of 18 patients no relationship between MTT and clinical symptoms was found. There is a good correlation between the clinical outcome at the time of discharge and the MTT. Clinical symptoms occurred if the MTT was between 3.2 and 4.0 s. An MTT above 4.0 s resulted in a bad clinical outcome. 9 of 18 patients showed angiographic criteria for endovascular treatment. All those patients showed an MTT of more than 3.2 s at the time of angiography.
CONCLUSION: The analysis of the cortical perfusion parameter MTT is suitable for revealing clinically relevant global and regional vasospasm. A risk potential prediction is possible. An MTT of 3.2 s indicates a conventional angiography (DSA). This should be verified using a larger number of patients.