Correlation Between Interictal Regional Cerebral Blood Flow and Depth-Recorded Interictal Spiking in Temporal Lobe Epilepsy

Summary: Purpose: Single photon emission computed tomography (SPECT) is used as an adjunctive method in preoperative localization of epileptic foci. In temporal lobe epilepsy (TLE), interictal hypoperfusion is observed in 60–70% of cases. Correlation with ictal EEG changes is observed in ∼50–60% of cases. Relationships with interictal EEG have been studied less. We compared interictal SPECT data obtained in 20 patients with their interictal intracerebral electrical activity recorded by depth electrodes to evaluate a potential relationship. Methods: We studied 20 sequential patients whose clinical, surface, and depth EEG data indicated seizure originating in the temporal lobe and who had interictal [99mTc]hexamethyl-propylene amine oxime (HMPAO)-SPECT stereo-EEG (SEEG). Intracerebral electrodes were placed according to the patient's profile. The interictal extent of epileptiform activity allowed delineation of the irritative zone. Interictal spike frequency was also analyzed semiquantitatively. Visual and numerical SPECT analysis was performed blind to SEEG data. Results: Interictal hypoperfusion was observed in 16 patients, involving the epileptogenic temporal lobe in 14. Except for 1 patient who manifested lateral temporal hypoperfusion corresponding to a mass lesion, two distinctive patterns of hypoperfusion were noted: (a) mesial hypoperfusion (5 patients), and (b) global temporal hypoperfusion (8 patients). In 8 patients, hypoperfusion had also extended into the adjacent cortex. Temporal mesial hypoperfusion was associated with spiking limited to the mesial structures, whereas global temporal hypoperfusion or hypoperfusion extending beyond the temporal lobe was associated with a similar topographic pattern of spikes. Conclusions: Comparison between SPECT and SEEG data collected in the interictal phase indicated that the extent of the hypoperfused area correlated topographically with that of the underlying irritative zone.