Abstracts

Rationale: Corpus callosotomy (CC) is a palliative surgical treatment for some patients with severe drug-resistant epilepsy, especially for those with generalized seizures. This surgical technique was developed based on the hypothesis that corpus callosum is the most important pathway for interhemispheric spread of epileptic activity and that severing this pathway would stop the rapid bilateral synchronization of epileptic discharges. If seizures still exist post-operationally, it could be observed that the seizure usually change from generalized to focal. This phenomenon provides opportunities to further localize the epileptogenic zone that could not be detected presurgically. Then, curative resection guided by stereoelectroencephalography (SEEG) can be conducted after total CC. Methods: From 2014 to 2019, 32 patients with non-resectable medical intractable epilepsy received total corpus callosotomy. Among them, 2 cases received secondary SEEG guided resective surgeries.Case 1. A female teenager developed epilepsy at 4 years of age, with bilateral axial and proximal tonic seizure 3-4 times per day. She had a past history of neonatal hypoxic ischemic encephalopathy. MRI images presented bilateral encephalomalacia, in which her left posterior focus was most remarkable. The electroencephalography (EEG) showed bilateral synchronic epileptic discharges. Total CC was performed at 12 years of age. After experience of more than 8 months of seizure free, the patient suffered refractory seizures again. From then on, the seizure semiology changed into bilateral asymmetric tonic or unilateral (left) arm tonic seizure, and unilateral diffuse or focal epileptic abnormalities were observed during video-EEG monitoring (Figure 1). Following a secondary presurgical evaluation, a group of SEEG electrodes were implanted. SEEG (Figure 2) showed diffuse interictal epileptic discharge in the left hemisphere and focal ictal onset in the parietal lobe (electrode L and M). Disconnection of left posterior portion combined with frontal cortectomy was performed successfully. Case 2. Similar to Case 1, a seven-year-old boy had a 5-year history of refractory daily seizure. The seizure semiology presented axial and proximal tonia. Both the encephalomalacia showed in MRI and the epileptic discharges showed in EEG were localized in the bilateral posterior portion of the brain. After CC, the epileptic focus of the tonic seizures was identifiable. Then a secondary SEEG guided resective surgery was conducted. Results: No neurological functional deficit or complication was observed except transient mutism in three patients. Twenty-nine patients were followed up for 1-5 years (mean 3.3 years). The rest 3 patients lost follow-up. The seizure outcomes were as follow: 9 cases (31%) of Engel Class I, 5 cases (17%) of Class II, 11 cases (38%) of Class III, 4 cases (14%) of Class IV. Both two SEEG cases described above showed outcomes of Class III after CC, but became seizure free (Class I) after SEEG guided resection. Conclusions: As a palliative surgical method, total CC is more effective than expected. Especially for some patients whose seizure change after CC from generalized or non-localized to focal one, additional SEEG guided resection can bring curative outcomes. Funding: No funding