[Positron emission tomography in two cases of transient global amnesia]

We encountered two cases of typical transient global amnesia (a 53-year-old woman and a 50-year-old man). Both cases showed no evidence of abnormal findings which caused the attack on examinations of CSF, EEG, brain CT, brain MRI and cerebral angiography. Examinations of positron emission tomography, using 15O labeled CO2 and O2, were performed on 14 and 8 days after the attack in the female and male cases, respectively, and those disclosed decreased regional blood flow (CBF), increased oxygen extraction ratio (OER), and decreased oxygen metabolic ratio (CMRO2) in the bilateral medial temporal and occipital lobes, which were supplied by the bilateral posterior cerebral arteries. PET, performed on about one month after the attack, revealed normalized values of CBF, OER, CMRO2 in both cases. These findings strongly suggested that transient global amnesia in our cases may be related to ischemia of the bilateral posterior cerebral arteries.