Focal cerebral hyperemia in postconcussive amnesia

Transient amnesia caused by minor head injury is commonly encountered in daily neurosurgical practice, but the mechanism of such amnesia has not been extensively studied. We measured the regional cerebral blood flow (rCBF) of patients with postconcussive amnesia with Xe/CT CBF to examine whether a focal disturbance of CBF exists. The Xe/CT CBF study was performed in eight patients with closed head injury without organic cerebral lesion while they were suffering from posttraumatic amnesia (concussion group). The time interval between accident and CBF measurement was less than 2 h in three patients, 5-6 h in two, 8-9 h in two, and 18 in one. The results were compared with those of nine normal volunteers and eight other age-matched patients who recovered without any neurological deficit despite the presence of hemorrhagic regions (mild hemorrhage group). The rCBF of the concussion group was significantly elevated in the bilateral mesial temporal cortex in comparison to the normal group. The rCBF in the mild hemorrhage group was lower than that of normal controls in all regions. The analysis of right-left difference in CBF indicated that there was significant asymmetry (right > left) in the frontal and temporal cortex in the concussion group, but not in the normal and mild hemorrhage group. This Xe/CT CBF study in acute stages of cerebral concussion, in which patients were amnestic, detected focal cerebral hyperemia. Such hyperemia in regions closely related to human memory function may be the result of vasoparalysis or the compensatory activation of memory circuits after denervation injury.