The usefulness of ictal SPECT for epilepsy surgery
Atsuko Matsuo1, Hiroshi Baba2, Tetsuo Matsuzaka1, Shigeki Tanaka3, Kenji Ono4
1Department of Pediatrics, Nagasaki University School of Medicine; 2Division of Neurosurgery and 3Division of Pediatrics, National Nagasaki Medical Center; 4Yokoo Hospital;
Purpose: For surgical intervention in patients with medically intractable epilepsy, it is essential to localize the epileptogenic focus. However, standard routine studies using MRI, interictal and ictal scalp EEGs, and intericatal SPECT often fail to delineate a plausible epileptogenic area. Some cases show no abnormalities or diffuse abnormalities in MRI. Scalp EEGs often provide limited information as well. Functional imaging techniques such as PET and SPECT may enable localization of the epileptogenic focus if they can reflect an ictal change in neuronal activities. Ictal SPECT is the only practical procedure that is currently available for examining an ictal state. In this study, we evaluated the usefulness of ictal SPECT in localizing the epileptogenic focus in patients who underwent resective surgery for medically intractable epilepsy compared to the usefulness of ictal scalp (including sphenoidal electrodes) EEG, interictal SPECT, and MRI.
Methods: We analyzed findings in(?) 17 patients (6 patients with temporal lobe epilepsy (T) and 11 patients with extra-temporal lobe epilepsy (ET)) who underwent resective surgery at the National Nagasaki Medical Center. The age at presurgical examination ranged from 2.5 months to 42 years. Ictal SPECT was performed during spontaneous seizures, and 99mTc-ECD was injected soon after seizure started. Ictal and interictal SPECT, ictal EEG, and MRI were performed on all patients. We defined gepileptogenic focush as the site that was determined by invasive methods, including ECoGs, and of which seizure ceased after resection, and we evaluated the rate of concordance
between the epileptogenic focus and the findings of each study.
Result: Brain MRI showed abnormal findings in 14 patients (T: 6, ET: 8). MRI lesions corresponded to the epileptogenc focus in 13 patients (T: 5 (73%), ET: 8 (83%)). One patient had bilateral hipocampal sclerosis, and 3 of the patients with ET showed no abnormalities on MR images. Ictal EEG provided information that enabled localization of the epileptogenic focus in only 10 patients (T: 4 (67%), ET: 6 (64%)). Interictal SPECT showed abnormal findings in 15 patients (T: 5, ET: 10). The epileptogenic foci were conformable in 13 of those is patients (T: 4 (67%), ET: 8 (73%)). On the other hand, ictal SPECT enabled detection of the epileptogenic focus in 16 patients (T: 6 (100%), ET: 10 (91%)). Fourteen patients (T: 4 ET: 10) showed definite focal hyperperfusion areas and three patients (T: 2, ET: 1) showed definite focal hypoperfusion areas in ictal SPECT. In the latter three patients, there might have been peri-lesional epileptogenicity and hyperperfusion, whereby high degree gliosis of the lesion was underscored as a hypoperfusional lesion. One patient in whom ictal SPECT did not enable detection of the epileptogenic focus had severe atrophy.
Conclusions: Ictal SPECT was the most sensitive and reliable procedure for delineating the epileptogenic focus in patients with medically intractable epilepsy. Ictal SPECT provided information indicating the possible location of the epileptic lesion even in some cases in which the epileptogenic focus could not be detected by MRI, ictal EEG or interictal SPECT. The necessity of invasive presurgical examination could be reduced by obtaining information on the localization of the epileptogenic focus by noninvasive means such as ictal SPECT.