Abstracts

Rationale: Corpus callosotomy has been considered as a palliative therapy for children with refractory epilepsy. After callosotomy, children with residual partial seizures and unilateral epileptiform discharges on electroencephalography (EEG) may be candidates for subsequent epilepsy surgery. Single photon emission computed tomography (SPECT) is a noninvasive technique that has shown promise in preoperative evaluation of focal epilepsies. This study aimed to evaluate localization of SPECT in patients with focal epilepsies after corpus callosotomy.Methods: Corpus callosotomy was performed for children with drop attacks or severe generalized convulsive seizures once no resectable focus could be identified through preoperative evaluations. SPECT using 99mTechnetium-ethyl cysteinate dimer (99mTc-ECD) was performed to investigate the area of hypoperfusion during the interictal phase when residual seizures evolved into partial onset after callosotomy. Patients with responsible focal abnormality on magnetic resonance imaging (MRI), such as tuberous sclerosis complex or focal cortical dysplasia, were excluded. Results: Among the 44 children under 15 years old who underwent callosotomy, ictal symptoms evolved into partial-onset seizures in 21 children after callosotomy. SPECT was performed in all 21 participants to investigate lesion localizability. Eleven of these 21 children demonstrated localized or lateralized perfusion. Initial seizures before callosotomy in these 11 children were epileptic spasms in 10, generalized tonic seizures in two, atypical absence in one, and complex partial seizures in one. Interictal SPECT exhibited no lateralization in eight children, and mild hypoperfusion of the temporal lobe in two, and of parietooccipital lobe in one. After callosotomy, residual seizures were classified as asymmetric epileptic spasms in five children, asymmetric tonic seizures in two, symmetric epileptic spasms in two, and symmetric tonic seizures in two. Post-callosotomy interictal EEG demonstrated epileptiform discharges unilaterally localized in the frontal region in nine children, in the posterior region in one and bilaterally multifocal discharges in one. Post-callosotomy interictal SPECT revealed hypoperfusion of the side of seizure onset in six children, and hyperperfusion in four. The remaining child demonstrated hyperperfusion of the seizure onset zone on ictal SPECT. Based on these findings, subsequent resective surgery of the unilateral frontal lobe was performed in three children and hemispheric/multilobar disconnective surgery in six. The remaining two children started vagus nerve stimulation. The interval between callosotomy and the second surgery ranged from 5 months to 10 years. At the latest evaluation after the final surgery, freedom from seizures (class I) had been accomplished in five children and favorable outcome (class I or II) achieved in four. Conclusions: ECD-SPECT after callosotomy for children with refractory epilepsy is useful for determining indications for subsequent epilepsy surgery.