A 77-year-old man with a history of radiation therapy for pharyngeal cancer and consequent asymptomatic left common carotid artery (CCA) occlusion showed asymptomatic ischemic stroke and left transient monocular blindness, and he was admitted to our hospital. He was found to have an indication for bypass surgery because of a remarkable reduction in cerebral blood flow in the ipsilateral middle cerebral artery (MCA) territory. Carotid ultrasonography revealed retrograde blood flow of the ipsilateral external carotid artery (ECA) and a U-turn phenomenon to the internal carotid artery (ICA). Cerebral angiography demonstrated spontaneous bonnet bypass flow from the right superficial temporal artery (STA) to the left STA, but the blood flow via the bypass was not enough to supply the left MCA. Bypass surgery to anastomose the bonnet bypass to the left MCA was performed, and postsurgical cerebral blood flow to the ipsilateral MCA territory improved. On STA duplex ultrasonography (STDU), the pulsatility index value of the contralateral STA changed from an ECA pattern before surgery to an ICA pattern after. Moreover, postsurgical mean flow velocity of the bonnet bypass to the left MCA was relatively higher than the presurgical retrograde mean flow velocity of the left STA. These ultrasonographic findings correlated with those on single photon emission computed tomography (SPECT) and cerebral angiography. As demonstrated in the present case, ultrasonography including STDU is useful in the evaluation of cerebral hemodynamics before and after cerebral artery bypass surgery and in the usual STA-MCA anastomosis.
