Postoperative transient neurological symptoms and chronic subdural hematoma after extracranial-intracranial bypass for internal carotid/middle cerebral atherosclerotic steno-occlusive diseases: negative effect on cognitive performance

Background: The mechanisms underlying post-extracranial to intracranial (EC-IC) bypass neurocognitive changes are poorly understood. Methods: Data from 55 patients who underwent a unilateral EC-IC bypass for atherosclerotic internal carotid artery (ICA)/middle cerebral artery (MCA) steno-occlusive disease were retrospectively evaluated. These patients underwent neuropsychological examinations (NPEs), including assessment by the Wechsler Adult Intelligence Scale-Third Edition and Wechsler Memory Scale-Revised (WMS-R) before and 6 months after EC-IC bypass. Results of NPEs were converted into Z-scores from which preoperative cognitive composite scores (CS_pre) and postoperative cognitive composite scores (CS_post) were obtained. The association between the change of composite score between pre- and postoperative NPEs (CS_post-pre = CS _post – CS _pre) and various variables were assessed. These latter variables included occluded artery (ICA or MCA), preexisting ischemic lesion as verified in preoperative T2WI, robust bypass patency as verified by MRA performed approximately 6 months postoperatively, and postoperative transient neurological symptoms and/or postoperative chronic subdural hematoma (CSDH), both of which were dichotomized as postoperative events. Results: Postoperative MRI follow-up (median, 6 months; interquartile range, 5–8 months) confirmed successful bypasses in all patients, with no additional ischemic lesions on T2WI when compared with preoperative imaging. Further, MRA showed patent bypasses in all patients. A nearly statistically significant CS _post-pre decrease was observed in patients with postoperative events when compared with those without postoperative events (−0.158 vs. 0.039; p = 0.069). A multiple regression model predicting CS_post-pre was performed. After controlling for occluded arteries, postoperative events were identified as an independent predictor of a decline in CS_post-pre (p = 0.044). In the group rate analysis, three of four postoperative NPE scores (Performance IQ, WMS-memory, WMS-attention) were significantly improved relative to preoperative NPE scores. Conclusions: Postoperative transient neurological symptoms and/or CSDH might play a significant role in the subtle decline in cognition following an EC-IC bypass. However, this detrimental effect was small, and based on the group rate analysis, we concluded that a successful unilateral EC-IC bypass does not adversely affect postoperative cognitive function.