We measured regional cerebral blood flow and cerebral vasoreactivity before and 3 months after carotid endarterectomy using xenon-133 inhalation with single-photon emission computed tomography and the acetazolamide test in 14 selected patients who had suffered cerebral transient ischemic attacks due to an ipsilateral internal carotid artery stenosis. The patients had neither clinical nor cerebral computed tomographic evidence of infarction. Baseline regional cerebral blood flow was symmetrical before and unchanged after endarterectomy. Before endarterectomy, vasoreactivity in the middle and anterior cerebral artery territories of the symptomatic side was significantly reduced (p<0.05); however, vasoreactivity was normalized 3 months after surgery. Our findings strongly suggest that the stenoses caused a reduction in perfusion reserve that was improved by carotid endarterectomy. A lthough carotid endarterectomy is one of the / \ most common vascular operations, 1 its effect -Z A . on cerebral blood flow (CBF) and intracranial hemodynamics have not been fully clarified. -10The diversity of results presumably reflects differences in studies with regard to patient selection, timing of the postoperative evaluation, and methodology used to measure CBF.The purposes of our study were to assess regional cerebral blood flow (rCBF) using xenon-133 inhalation and single-photon emission computed tomography (SPECT) and cerebral vasoreactivity using the carbonic anhydrase inhibitor acetazolamide 11 before and 3 months after carotid endarterectomy. Subjects and MethodsWe studied 14 patients (12 men and two women) aged 52-70 (mean 62) years. They had experienced cerebral transient ischemic attacks (TIA) due to ipsilateral internal carotid artery (ICA) stenosis, and they were treated with carotid endarterectomy. The interval from the last TIA to endarterectomy varied from 10 to 33 (median 15) days. Patients who had a history of stroke, clinical findings suggestive of cere- Received May 17, 1989; accepted February 28, 1990. bral infarction, or cerebral computed tomographic evidence of infarction were excluded. The patients had experienced no symptoms from the contralateral cerebral hemisphere or the brain stem. This selection was made in order to exclude the effects of cerebral infarction on the rCBF studies. No patient had orthostatic provoked symptoms. The study was performed in accordance with the Helsinki Declaration, and informed consent was given by all patients. Stenosis was assessed preoperatively using conventional arteriography and pulsed Doppler ultrasound studies.12 Three stenoses (22%) reduced the diameter of the ICA by 50%-75%, two (14%) by 75%-90%, and the remaining nine (64%) by >90%. Ten stenoses were in the left and the other four were in the right ICA. In the contralateral ICA, a stenosis of <50% was found in three patients, a stenosis of 75% in one patient, and a stenosis of 90% in another; the contralateral ICA was occluded in two patients and normal in the remaining seven (50%). One patient had a vertebral...