Regional cerebral hemodynamics during re-build up phenomenon. Analysis by using 99mTc-HMPAO SPECT

The re-build up phenomenon is the characteristic EEG finding following hyperventilation in childhood moyamoya disease. This study evaluated the role of cerebral blood flow (CBF) associated with this phenomenon using single photon emission CT (SPECT) with Tc-99m hexamethyl propylene amine oxime (Tc-99m HMPAO). The subjects were each two adult and pediatric patients. Tc-99m HMPAO (10 mCi) was injected immediately after 4-min hyperventilation. After the initial scanning, an additional 20 mCi of Tc-99m HMPAO was iv injected for the second scanning. Xe-133 SPECT was also performed for the evaluation of resting CBF. The re-build up phenomenon was observed preoperatively in one patient, which originated from the bilateral parieto-occipital area one min after hyperventilation and extended to the entire hemisphere 30 sec later. SPECT did not reveal severe ischemia in the entire hemisphere after hyperventilation, but revealed a marked CBF decrease in the bilateral parieto-occipital lobe. The patient underwent bilateral STA-MCA anastomosis combined with encephalo-duro-arterio-myo-synangiosis. Postoperative examination revealed no evidence of build-up phenomenon on EEG or abnormal perfusion reserve on Xe-133 SPECT. Nor was marked CBF decrease observed after hyperventilation on Tc-99m SPECT. These findings suggest that regional CBF decrease may play a critical role in the appearance of the re-build up phenomenon on EEG, as well as hypoxic hypoxia after hyperventilation. (N.K.)