Hyperperfusion syndrome following carotid endarterectomy: evaluation using diffusion-weighted magnetic resonance imaging--case report.

A 65-year-old female developed hyperperfusion syndrome following carotid endarterectomy for severe stenosis of the left internal carotid artery. Transcranial Doppler monitoring showed a sharp increase in flow velocity in the middle cerebral artery (MCA). Diffusion-weighted magnetic resonance (MR) imaging demonstrated diffuse hyperintensity in the region of the left MCA, which diminished markedly 9 days later. The abnormal hyperintensity decreased as the patient's symptoms improved, suggesting that diffusion-weighted MR imaging can be used for evaluating the course of hyperperfusion syndrome.