Pathological findings underlying focal temporal lobe hypometabolism in partial epilepsy

Histopathological studies were carried out on temporal lobe tissue from 25 patients with partial complex seizures who were studied by interictal positron computed tomography (PCT) with 18F-fluorodeoxyglucose and subsequently underwent anterior temporal lobe resection. Abnormalities were identified on x-ray computed tomographic scans in 7 patients, but none indicated the site of a pathologically confirmed structural lesion. Hypometabolic zones were observed on PCT scans of 22 patients and corresponded to focal pathological abnormalities in 19 (15 mesial temporal sclerosis, 2 small neoplasms, 1 angioma, 1 heterotopia). In 1 patient with a focally abnormal PCT scan and no pathological changes, the lesion may have been located posterior to the resection. In the remaining 2 patients, the hypometabolic zones later disappeared and may have represented a transient response induced by depth electrode implantation. Three patients with normal PCT scans had no pathological abnormalities in their resected tissue. The degree of relative hypometabolism measured by PCT correlated well with the severity of the pathological lesion, but the size of the hypometabolic zone was generally much larger than the area of pathological involvement. This discrepancy could not be considered an artifact of technique and must represent either structural abnormalities below the resolution of routine histopathological studies (e.g., loss of synapses) or functional inactivation of neuronal elements associated with the epileptogenic lesion.