Postoperative alteration in cerebral blood flow, glucose metabolism and benzodiazepine receptor binding potential in temporal lobe epilepsy

Abstract

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Objectives: I-123 iomazenil(IMZ), a specific ligand for the central benzodiazepine receptor(BZR), is useful to detect epileptogenic foci. We expect that IMZ can also demonstrate neuronal viability even in hypoperfused and hypometabolic areas. To evaluate the alteration of central BZR density, cerebral blood flow and glucose metabolism after selective resection of mesial temporal area, we compared the changes in the distributions of I-123 IMZ, Tc-99m ECD (ECD) and F-18 FDG (FDG) between pre- and postoperative states in patients with unilateral temporal lobe epilepsy (TLE).

Methods: Six patients (4 men, 2 women; age 16-60 yr) with unilateral mesial TLE underwent PET and SPECT scans as preoperative examination, and they repeated the scans 6 months after the selective surgery. They have since been free of seizures. IMZ SPECT was performed for 30 min, started 3 hours after administering 222 MBq of IMZ, FDG PET for 10 min, started 45 min after administering 296 MBq of FDG, and ECD SPECT for 30 min after administering 740 MBq of ECD. PET and SPECT images were anatomically standardized using SPM99, and segmented into 7 template ROIs (frontal, superior parietal, inferior parietal, mesial temporal, lateral temporal, occipital and cerebellum) based on brain mapping using a stereotaxic ROI template. We calculated ipsilateral/contralateral counts ratios in each ROIs. In unilateral TLE patients, we considered the contralateral side as control. And we compared ipsilateral/contralateral ratios between pre- and postoperative states using student paired t test.

Results: In the mesial and lateral temporal lobe, IMZ, ECD SPECT and FDG PET showed statistically significant differences in ipsilateral/contralateral ratios between pre- and postoperative states. In the occipital lobe, IMZ SPECT did not show a significant difference between pre- and postoperative states (p=0.084), while ECD SPECT and FDG PET showed statistically significant differences (ECD; p=0.008, FDG; p=0.046).

Conclusions: A discrepancy was observed in the occipital lobe between IMZ and FDG/ECD after the unilateral TLE surgical therapy. Decreases in cerebral blood flow and glucose metabolism suggested a remote effect caused by neural disconnection. On the other hand, unchanged IMZ uptake in this area implied that the nerve cells were viable as shown by the preservation of benzodiazepine receptors. This study demonstrated that surgical resection in TLE can affect wide spread suppression in glucose metabolism and blood flow, but that neuronal damage is restricted only in the neighboring structure of resection.