Abstracts

Rationale: Perfusion brain SPECT (Single photon emission computed tomography) shows a snap shot of regional cerebral blood flow (rCBF) pattern at the time of radiotracer injection. Ictal SPECT with radiotracer injecton during clinical seizure shows rapid rCBF changes accompanying focal seizures. The propagation of ictal discharges from one temporal lobe directly to contralateral temporal lobe is not uncommonly observed during seizures of mesial temporal lobe epilepsy (mTLE). To investigate the rCBF changes in the mTLE with ictal EEG spreading to contralateral temporal lobe, we retrospectively analyzed ictal EEG and SPECT of 5 patients. Methods: Five patients (mean age 31.8± 7.2; 2 women) with unilateral mTLE were included. All patients showed unilateral hippocampal sclerosis on brain MRI. Patients’ seizures and EEG were continuously monitored in epilepsy monitoring unit, and the radiotracer 99mTc-ethylcysteinate dimer was injected for ictal SPECT as soon as possible after clinical or EEG seizure was witnessed. An interictal SPECT study was performed when the patient had been seizure free for more than previous 24 hours. We analyzed the positive result (reflecting increased rCBF during seizure) and negative result (decreased rCBF during seizure) of SISCOM (Subtraction Ictal SPECT co-registered to MRI). Results: Four patients had left mTLE with ictal EEG onset from left temporal lobe and left hippocampal sclerosis, and the remaining one had right mTLE. All seizures were complex partial seizures, and the mean duration of EEG seizures was 79.0± 32.8 seconds. In all patients, the radiotracer was injected after ictal EEG was propagated to the contralateral temporal lobe. The average delay between ictal onset and radiotracer injection was 29.7± 9.6 seconds. The positive results of SISCOM images showed hyperperfusion on the contralateral temporal lobe to the ictal EEG onset, along with ictal EEG build-up on that side. However, the negative results of SISCOM images demonstrated hypoperfusion on the epileptogenic temporal lobe in three patients, and no significantly lateralized rCBF changes in two patients. Conclusions: Our study demonstrates increased rCBF on the contralateral temporal lobe whereas decreased rCBF on the ipsilateral temporal lobe during mTLE seizures with ictal EEG propagated to the contralateral side.