Abstracts

Rationale: Corpus callosotomy has been considered as a palliative therapy for drug-resistant epilepsy. The principal candidates for this procedure are epileptic patients in whom no resectable seizure focus can be identified. Benefits have been shown for patients, particularly children, with disabling drop attacks. Conversely, residual seizures are often observed postoperatively, even in patients free from drop attacks. These are usually milder forms of seizure and occur less frequently than preoperatively. In addition, EEG often reveals localized or lateralized epileptiform discharges after corpus callosotomy. These findings suggest that corpus callosotomy is a diagnostic as well as palliative therapy, and some patients who undergo this procedure may ultimately be candidates for resective surgery. No larger series of corpus callosotomy and subsequent resective surgery has been performed. The experiences with this stepwise procedures were thus reviewed. Methods: Between 1987 and 2008, 169 patients received corpus callosotomy. These included 132 children <15 years old. Of these, resective or disconnective surgery was performed in 16 patients in whom post-callosotomy EEG showed localized or lateralized epileptiform discharges responsible for residual partial seizures. Twelve patients underwent invasive EEG monitoring using implanted subdural electrodes and resective/disconnective surgery of the frontal lobe. The remaining 4 patients received multilobar disconnection surgery including hemispherotomy and posterior quadrantectomy, dependent on neurological condition and findings from MRI and scalp EEG. Medical records and EEG data were reviewed and analyzed. Postoperative seizure frequency was followed for 6-96 months. Results: Initial MRI showed no lesion in 11 patients, atrophic lesion in 3 (localized to frontal lobe in 1 case and diffuse in 2 cases), tuberous sclerosis in 1, and multilobar cortical dysplasia in 1. Before corpus callosotomy, bilaterally synchronous epileptiform discharges were observed on EEG in all cases. In 3 patients with atrophic lesions on MRI, amplitude of EEG discharges was inversely dominant in the non-affected hemisphere. Post-callosotomy EEG demonstrated localized/lateralized epileptiform discharges responsible for residual partial seizures in all cases. After second surgery, freedom from seizure was obtained in 8 patients (4 without lesion, 3 with atrophic lesion, and 1 with tuberous sclerosis). Conclusions: Half of patients became seizure-free after corpus callosotomy and subsequent surgery in our pediatric series. This result shows little difference from that in series for simple resective surgery. Although corpus callosotomy is a palliative method, complete seizure control may be achieved with subsequent surgery in some patients. Even in cases of suspected partial epilepsy, such as patients with unilateral atrophic lesion who should be candidates for lobectomy or hemispherotomy, the epileptogenic area responsible for persisting seizure may only become evident on EEG after callosotomy. This stepwise procedure would lead to accurate and safe outcomes in these patients.