Evaluation of cerebral hemodynamic in patients with subarachnoid hemorrhage: the role of perfusion computed tomography

Background and Purpose - Subarachnoid hemorrhage due to the rupture of an intracranial aneurysm (aSAH) is a devastating disease with a mortality rate of nearly 50% and with an additional 30% of patients requiring long-term care. Delayed cerebral ischemia and subsequent cerebral infarction are the leading causes of poor outcome. The alterations of cerebral hemodynamic due to aSAH are caused by the interaction of many mechanisms including the early impact of bleeding on the brain, the impairment of cerebral autoregulation and the cerebral vasospasm. In this study we used the Perfusion Computed Tomography Scan (PCT scan) to evaluate the time course of the cerebral perfusion changes over the first two weeks after bleeding. We also attempted to identify the parameters of the perfusion that were associated with the development of cerebral vasospasm and infarction. Methods - Forty patients with aSAH underwent PCT scans according to regular intervals of time from SAH (0-3 days, 4-7 days, 8-11 days and later). A total number of 92 Perfusion CT studies (2.3 per patient) were carried out and ACA and MCA territory were studied. Out of 40 patients, 22 patients did not develop symptomatic vasospasm and 18 patients developed symptomatic vasospasm, with cerebral infarction in 8 of them. We analyzed the global cerebral perfusion using the mean value ( SD) obtained by the average of the values of each parameter (CBV, CBF and MTT) in each group of patients and in the established intervals of time. The changes of CBV, CBF and MTT over time for each group of patients were analysed and the values of the three groups in each interval of time were compared. Results - Patients without vasospasm have little changes, and patients with symptomatic vasospasm have no changes of the perfusion values throughout the study. On the contrary, in patients with symptomatic vasospasm and cerebral infarction, CBV and CBF reach the maximum value in the interval between 4 and 7 days and decrease in the following days and MTT is stable in the first two intervals of time. These values can represent the effect of the hemodynamic intervention in patients who have an impairment of cerebral autoregulation in a stage before the onset of vasospasm. The reason of this is that a preventive mild volume expansion was started immediately after the aneurysm treatment in all patients. These patients have a decrease of CBV value and a significant decrease of CBF value (p=0.016) between 8 and 11 days and in the later interval the CBF value is persistently significantly lower than in the interval between 4 and 7 days (p=0.044). Between 8 and 11 days, in the comparison with the group of patients without vasospasm, they have a significantly lower value of CBF (p=0.035). Moreover the MTT reaches the maximum value between 8 and 11 days and it is significantly higher (p=0.031) than in patients without vasospasm in the same interval of time. Conclusions - Our results suggest that patients who experienced ischemic deficits and cerebral infarction have an impairment of cerebral autoregulation before the onset of vasospasm and that they can be studied using the Perfusion CT scan.