Extracranial-Intracranial Arterial Bypass in a Case of Internal Carotid Artery Occlusion: Evaluation of Cerebrovascular Reactivity Using Acetazolamide Challenge and CT Perfusion

Internal carotid artery (ICA) occlusions can be acute or chronic and result in different clinical outcomes. Chronic ICA occlusions are tolerated differently by individuals. If the dependent brain tissue is adequately supplied by collaterals, chronic ICA occlusions may be asymptomatic or oligosymptomatic. If collateral supply is marginal or inadequate, cerebral ischemia may occur spontaneously or under the influence of precipitating factors such as arterial hypotension, blood loss, or dehydration. We report the case of a 67-year-old woman who presented to the emergency department with subacute dysarthria, discrete motor impairment of the left arm, and latent left facial nerve palsy. Her symptoms were completely resolved at the time of medical examination. Her medical history was unremarkable except for arterial hypertension. Initial MRI showed multiple small embolic infarcts in the right hemisphere and occlusion of the right cervical ICA segment due to dissection, which was confirmed by subsequent DSA. Follow-up DSA after conservative medical therapy showed persistent chronic occlusion of the right ICA with moderate collateralization of the right MCA territory. Initial functional assessment of cerebral hemodynamics by computed tomography perfusion (CTP) and acetazolamide challenge showed preserved cerebrovascular reactivity (CVR). However, the subsequent CTP study showed a decrease in CVR and only moderate collateralization as demonstrated by DSA. The decision was made to perform revascularization by bypass surgery. The evaluation of cerebrovascular reserve capacity using CTP and acetazolamide challenge to select potential candidates who would benefit from extracranial/intracranial (EC/IC) bypass surgery for ICA occlusion is the main topic of this chapter.