Is 11C-flumazenil PET superior to 18FDG PET and 123I-iomazenil SPECT in presurgical evaluation of temporal lobe epilepsy?

OBJECTIVE: To determine the contribution of 18FDG PET, 11C-flumazenil PET, and 123I-iomazenil SPECT to the presurgical evaluation of patients with medically intractable complex partial seizures.
METHODS: Presurgical evaluation was performed in 23 patients, who were considered candidates for temporal lobe resective surgery (14 females and nine males with a median age of 34 (range 13 to 50) years). The presurgical diagnosis was based on seizure semiology as demonstrated with ictal video recording, ictal and interictal scalp EEG recordings, and MRI.
RESULTS: Eighteen patients had convergent findings in clinical semiology, interictal and ictal EEG with scalp and sphenoidal electrodes, and MRI that warranted surgery without depth EEG (DEEG). In five patients with insufficient precision of localisation, DEEG with intracerebral and subdural electrodes was performed. MRI showed abnormalities in 22 out of 23 patients. Of these 22, 18 had mesial temporal sclerosis. This was limited to the mesial temporal lobe in four and more widespread in the temporal lobe in 14 patients. In one patient only enlargement of the temporal horn was found and in three others only white matter lesions were detected. 18FDG PET showed a large area of glucose hypometabolism in the epileptogenic temporal lobe, with an extension outside the temporal lobe in 10 of 23 patients. Only in one of these patients DEEG showed extratemporal abnormalities that were concordant with a significant extratemporal extension of hypometabolism in 18FDG PET. 18FDG PET was compared with the results of scalp EEG: in none of the patients was an anterior temporal ictal onset in scalp EEG related to a maximum hypometabolism in the mesial temporal area. By contrast, the region of abnormality indicated by 11C-flumazenil PET was much more restricted, also when compared with DEEG findings. Extension of abnormality outside the lobe of surgery was seen in only two patients with 11C-flumazenil and was less pronounced compared with the intratemporal abnormality. Both 18FDG PET and 11C-flumazenil PET reliably indicated the epileptogenic temporal lobe. Thus these techniques provide valuable support for the presurgical diagnosis, especially in patients with non-lesional MRI or non-lateralising or localising scalp EEG recordings. In those patients in whom phase 1 presurgical evaluation on the basis of classic methods does not allow a localisation of the epileptogenic area, PET studies may provide valuable information for the strategy of the implantation of intracranial electrodes for DEEG. Previous studies have suggested that 11C-flumazenil binding has a closer spatial relationship with the zone of ictal onset than the area of glucose hypometabolism, but this study suggests rather that the decrease in the 11C-flumazenil binding simply reflects a loss of neurons expressing the benzodiazepine-GABA receptor. 11C-flumazenil PET did not prove to be superior to 18FDG PET.
CONCLUSION: In 21 patients sufficient material was obtained at surgery for a pathological examination. In 17 mesial temporal sclerosis, in one an oligodendroglioma grade B, in another a vascular malformation and in two patients no abnormalities were found. Although all 21 patients with pathological abnormality showed hypometabolic zones with 18FDG PET and a decreased uptake in 11C-flumazenil binding, there was no strong correlation between pathological diagnosis and functional abnormal areas in PET. Grading of medial temporal sclerosis according to the Wyler criteria showed no correlation with the degree of hypometabolism in either 18FDG or 11C-flumazenil PET. The interictal 123I-iomazenil SPECT technique was highly inaccurate in localising the lobe of surgery.