Change in brain perfusion after extracranial–intracranial bypass surgery detected using the mean transit time of computed tomography perfusion

Background: Cerebral perfusion can be evaluated using a computed tomography (CT) scan by intravenous bolus injection of contrast media. The purpose of this study was to investigate the value of CT perfusion (CTP) in follow-up of extracranial–intracranial (EC-IC) bypass surgery. Methods: We retrospectively reviewed pre- and postoperative CTP studies in 14 patients who received EC-IC bypass surgery because of cerebral arterial occlusion or stenosis. Brain areas showing prolongation of the mean transit time (MTT) were automatically identified and quantitatively measured. Results: All 14 patients showed MTT prolongation in the preoperative CTP study. In 13 patients, a reduction in brain volume with MTT prolongation was noted during postoperative CTP. These 13 patients had a patent EC-IC anastomosis, and 42 ± 21% of the brain area with MTT prolongation returned to normal MTT during CTP 7 ± 4 days (range 2–13 days) after surgery. On clinical follow up of 41 ± 16 months (range 14–60 months), no stroke or transient ischemic attack was noted after bypass surgery in these 13 patients. The brain volume with MTT prolongation did not decrease in just one patient whose EC-IC anastomosis was not patent, and the patient suffered a minor stroke during surgery. Conclusion: Quantitative results for the brain area with MTT prolongation were positively correlated with improvement in brain perfusion shown on MTT, EC-IC bypass patency, and patient outcome