Response to Letter by Juvela et al
We thank Juvela et al for their comment on our article about silent and symptomatic ischemia after aneurysm clipping.1 Our article focuses on the incidence of silent and symptomatic infarction directly related to microsurgical clipping. We are aware that there exist several articles on postsubarachnoid hemorrhage cerebral infarctions. The reported investigations were mainly done by serial CT scans, which can only detect infarction areas >5 mm. Moreover, most patients in these studies underwent cerebral angiography before the aneurysm treatment, which itself has a rate of silent ischemic events of 23%.2 An evaluation of silent ischemia related to the surgical procedure by diffusion-weighted MRI has not been performed to our knowledge.
Our infarction rate cannot be compared with earlier series done with CT scans because most of our infarctions are not detectable by CT scan. We combined ruptured and unruptured aneurysms because we just focused on the clipping process. It is clear that the overall infarction rate of ruptured aneurysm is higher due to the fact of subarachnoid hemorrhage.
We agree that univariant analysis to compare 2 populations (with or without stroke) is not absolutely clear. Indeed this corresponds statistically to a Student t test between 2 populations (with or without stroke). That said, the t test using bilateral and unequal variance between the population with and without stroke gives exactly the same results (probability value); therefore, most importantly, the conclusions of the study and the statistical analysis remain exact.